Singular:           Plural:

abyss               abysses

alumnus         alumni

analysis          analyses

aquarium        aquaria

arch                 arches

atlas                atlases

axe                  axes

baby                babies

bacterium       bacteria

batch               batches

beach              beaches

brush               brushes

bus                  buses

calf                  calves

chateau          chateaux

cherry              cherries

child                children

church             churches

circus              circuses

city                   cities

cod                  cod

copy                copies

crisis               crises

curriculum     curricula

deer                 deer

dictionary       dictionaries

domino          dominoes

dwarf               dwarves

echo               echoes

elf                    elves

emphasis      emphases

family              families

fax                   faxes

fish                  fish

flush                flushes

fly                     flies

foot                  feet

fungus            fungi

half                  halves

hero                 heroes

hippopotamus  hippopotami

hoax                hoaxes

hoof                 hooves

index                indexes

iris                    irises

kiss                  kisses

knife                 knives

lady                  ladies

leaf                  leaves

life                   lives

loaf                  loaves

man                 men

mango             mangoes

memorandum   memoranda

mess                messes

moose             moose

motto               mottoes

mouse              mice

nanny               nannies

neurosis          neuroses

nucleus            nuclei

oasis                oases

octopus           octopi

party                 parties

pass                 passes

penny               pennies

person             people

plateau             plateaux

poppy               poppies

potato              potatoes

quiz                  quizzes

reflex                reflexes

runner-up        runners-up

scarf                scarves

scratch             scratches

series               series

sheaf                sheaves

sheep               sheep

shelf                 shelves

son-in-law       sons-in-law

species            species

splash              splashes

spy                    spies

stitch                 stitches

story                 stories

syllabus          syllabi

tax                    taxes

thesis              theses

thief                 thieves

tomato            tomatoes

tooth                teeth

tornado           tornadoes

try                     tries

volcano           volcanoes

waltz                waltzes

wash               washes

watch              watches

wharf               wharves

wife                  wives

woman           women

Some nouns have identical singular and plural. Many of these are the names of animals:

bison

buffalo

deer

duck

fish

pike

salmon

sheep

squid

swine

trout

Apophonic plurals

The plural is sometimes formed by simply changing the vowel sound of the singular (these are sometimes called mutated plurals):

foot	feet
goose	geese
louse	lice
dormouse	dormice
man	men
mouse	mice (computer mouse can also take the regular plural form mouses)
tooth	teeth
woman	women /ˈwɪmᵻn/

This group consists of words that historically belong to the Old English consonant declension. There are many compounds of man and woman that form their plurals in the same way: postmen, policewomen, etc.

The plural of mongoose is mongooses. Mongeese is a back-formation by mistaken analogy to goose / geese and is often used in a jocular context. The form meese is sometimes also used humorously as the plural of moose — normally moose or mooses — or even of mouse.

Irregular plurals from Latin and Greek

• Final a becomes -ae (also -æ), or just adds -s:

alumna	alumnae
formula	formulae/formulas
encyclopaedia (or encyclopædia) / encyclopedia	encyclopaedias / encyclopedias (encyclopaediae and encyclopediae are rare)

Scientific abbreviations for words of Latin origin ending in -a, such as SN for supernova, can form a plural by adding -e, as SNe for supernovae.

• Final ex or ix becomes -ices (pronounced /ᵻsiːz/), or just adds -es:

index	indices	/ˈɪndᵻsiːz/	or indexes
matrix	matrices	/ˈmeɪtrᵻsiːz/
vertex	vertices	/ˈvɜːrtᵻsiːz/

Some people treat process as if it belonged to this class, pronouncing processes /ˈprɒsᵻsiːz/ instead of standard /ˈprɒsɛsᵻz/. Since the word comes from Latin processus, whose plural in the fourth declension is processūs with a long u, this pronunciation is by analogy, not etymology.

• Final is becomes es (pronounced /iːz/):

axis	axes	/ˈæksiːz/
genesis	geneses	/dʒɛn.ə.siːz/
nemesis	nemeses	/ˈnɛməsiːz/
crisis	crises	/ˈkraɪsiːz/
testis	testes	/ˈtɛstiːz/

(Some of these are Greek rather than Latin words, but the method of plural formation happens to be the same.)

Axes (/ˈæksiːz/), the plural of axis, is pronounced differently from axes (/ˈæksᵻz/), the plural of ax(e).

• Final ies remains unchanged:

series	series
species	species

Specie for a singular of species is considered nonstandard. It is standard meaning the form of money, where it derives from the Latin singular ablative in the phrase in specie.

• Final um becomes -a, or just adds -s:

addendum	addenda
agendum (obsolete, not listed in most dictionaries)	agenda means a “list of items of business at a meeting” and has the plural agendas
corrigendum	corrigenda
datum	data (Now usually treated as a singular mass noun in both informal and educated usage, but usage in scientific publications shows a strong American/British divide. American usage generally prefers to treat data as a singular in all contexts, including in serious and academic publishing. British usage now widely accepts treating data as singular in standard English, including educated everyday usage at least in non-scientific use. British scientific publishing usually still prefers treating data as a plural. Some British university style guides recommend using data for both the singular and the plural use and some recommend treating it only as a singular in connection with computers.) In engineering, drafting, surveying, and geodesy, and in weight and balance calculations for aircraft, a datum (plural datums or data) is a reference point, surface, or axis on an object or the Earth’s surface against which measurements are made.
forum	fora/forums (fora is rare and might only be used to refer to more than one original Roman forum.)
medium	media (in communication systems and digital computers. This is now often treated as a singular mass noun); mediums (spiritualists, or items of medium size)
memorandum	memoranda/memorandums
millennium	millennia
ovum	ova
referendum	referendums is often taken to mean plebiscites, and referenda as the propositions voted on. It is often argued that referenda is incorrect because it is a Latin gerund, which did not have a plural form, while the “propositions voted on” is more like a gerundive, which could be pluralised.
spectrum	spectra (as in power spectrum in electrical engineering)

• Final us becomes -i (second declension, [aɪ]) or -era or -ora (third declension), or just adds -es (especially for fourth declension words, where the Latin plural was similar to the singular):

alumnus	alumni
corpus	corpora
census	censuses
focus	foci
genus	genera
prospectus	prospectuses (plural prospectus is rare although correct in Latin)
radius	radii
campus	campuses (The Latinate plural form campi is sometimes used, particularly with respect to colleges or universities; however, it is sometimes frowned upon. By contrast, the common plural form campuses is universally accepted.)
succubus	succubi (The word omnibus is similar in form but is originally dative plural, so cannot be pluralised to *omnibi: see The Motor Bus.)
stylus	styli
syllabus	syllabi/syllabuses (in fact the Latin plural is syllabūs)
viscus	viscera
virus	viruses ( see Plural form of words ending in -us#Virus )

cactus	cactuses/cacti (in Arizona many people avoid either choice with cactus as both singular and plural.)
fungus	fungi
hippopotamus	hippopotamuses/hippopotami
octopus	octopuses (note: octopi also occurs, although it is strictly speaking unfounded, because it is not a Latin noun of the second declension, but rather a Latinized form of Greek ὀκτώ-πους, eight-foot. The theoretically correct form octopodes is rarely used.)
platypus	platypuses (same as octopus: platypi occurs but is etymologically incorrect, and platypodes, while technically correct, is even rarer than octopodes.)
terminus	termini/terminuses
uterus	uteri/uteruses

• Final us remains unchanged in the plural (fourth declension – the plural has a long ū to differentiate it from the singular short ǔ):

meatus	meatus (but usually meatuses)
status	status (but usually statuses)

Colloquial usages based in a humorous fashion on the second declension include Elvii (better Latin would be Elvēs or Elvidēs) to refer to multiple Elvis impersonators and Loti, used by petrolheads to refer to Lotus automobiles in the plural.

Some Greek plurals are preserved in English (cf. Plurals of words of Greek origin):

• Final on becomes -a:

automaton	automata
criterion	criteria
phenomenon	phenomena
polyhedron	polyhedra

• Final as in one case changes to -antes:

Atlas	Atlantes (statues of the Titan); but
atlas	atlases (map collections)

• Final ma in nouns of Greek origin can become -mata, although -s is usually also acceptable, and in many cases more common.

stigma	stigmata/stigmas
stoma	stomata/stomas
schema	schemata/schemas
dogma	dogmata/dogmas
lemma	lemmata/lemmas
anathema	anathemata/anathemas

Irregular plurals from other languages

• Some nouns of French origin add an -x, which may be silent or pronounced /z/:

beau	beaux or beaus
bureau	bureaux or bureaus
château	châteaux or châteaus
tableau	tableaux or tableaus

• Italian nouns, notably technical terms in music and art, often retain the Italian plurals:

cello

celli

Foreign terms may take native plural forms, especially when the user is addressing an audience familiar with the language. In such cases, the conventionally formed English plural may sound awkward or be confusing.

• Nouns of Slavic origin add -a or -i according to native rules, or just -s:

kniazhestvo	kniazhestva / kniazhestvos
kobzar	kobzari / kobzars
oblast	oblasti / oblasts

• Nouns of Hebrew origin add -im or -ot (generally m/f) according to native rules, or just -s:

cherub	cherubim / cherubs
seraph	seraphim / seraphs (The Hebrew singular is “saraph”. “Seraph” is a back-formation from “seraphim”. The form “seraphims” occurs in the King James Version.)
matzah	matzot / matzahs
kibbutz	kibbutzim / kibbutzes

Ot is pronounced os (with unvoiced s) in the Ashkenazi dialect.

• Many nouns of Japanese origin have no plural form and do not change:

bentō	bentō
otaku	otaku
samurai	samurai

Other nouns such as kimonos, ninjas, futons, and tsunamis are more often seen with a regular English plural.

• In New Zealand English, nouns of Māori origin can either take an -s or have no separate plural form. Words more connected to Māori culture and used in that context tend to retain the same form, while names of flora and fauna may or may not take an -s, depending on context. Many regard omission as more correct:

kiwi	kiwi/kiwis
kowhai	kowhai/kowhais
Māori	Māori/(occasionally Māoris)
marae	marae
tui	tuis/tui
waka	waka

Plurals of compound nouns

The majority of English compound nouns have one basic term, or head, with which they end. These are nouns and are pluralized in typical fashion:

able seaman	able seamen
head banger	head bangers
yellow-dog contract	yellow-dog contracts

Some compounds have one head with which they begin. These heads are also nouns and the head usually pluralizes, leaving the second, usually a post-positive adjective, term unchanged:

attorney general	attorneys general
bill of attainder	bills of attainder
court martial	courts martial
director general	directors general
fee simple absolute	fees simple absolute
governor-general	governors-general
passerby	passersby
ship of the line	ships of the line
son-in-law	sons-in-law
minister-president	ministers-president
chief of staff	chiefs of staff
procurator fiscal (in Scotland)	procurators fiscal

It is common in informal speech to pluralize the last word instead, like most English nouns, but in edited prose aimed at educated people, the forms given above are preferred.

If a compound can be thought to have two heads, both of them tend to be pluralized when the first head has an irregular plural form:

man-child	men-children
manservant	menservants
woman doctor	women doctors (no longer in common use)

Two-headed compounds in which the first head has a standard plural form, however, tend to pluralize only the final head:

city-state	city-states
nurse-practitioner	nurse-practitioners
scholar-poet	scholar-poets

In military usage, the term general, as part of an officer’s title, is etymologically an adjective, but it has been adopted as a noun and thus a head, so compound titles employing it are pluralized at the end:

brigadier general	brigadier generals
major general	major generals

For compounds of three or more words that have a head (or a term functioning as a head) with an irregular plural form, only that term is pluralized:

man-about-town	men-about-town
man-of-war	men-of-war
woman of the street	women of the street

For many other compounds of three or more words with a head at the front — especially in cases where the compound is ad hoc or the head is metaphorical — it is generally regarded as acceptable to pluralize either the first major term or the last (if open when singular, such compounds tend to take hyphens when plural in the latter case):

ham on rye	hams on rye/ham-on-ryes
jack-in-the-box	jacks-in-the-box/jack-in-the-boxes
jack-in-the-pulpit	jacks-in-the-pulpit/jack-in-the-pulpits

With a few extended compounds, both terms may be pluralized—again, with an alternative (which may be more prevalent, e.g. heads of state):

head of state	heads of states/heads of state
son of a bitch	sons of bitches/sons-of-a-bitch

With extended compounds constructed around o, only the last term is pluralized (or left unchanged if it is already plural):

cat-o’-nine-tail	cat-o’-nine-tails
jack-o’-lantern	jack-o’-lanterns
will-o’-the-wisp	will-o’-the-wisps

Plurals without singulars

Some nouns have no singular form. Such a noun is called a plurale tantum. Examples include cattle, thanks, clothes (originally a plural of cloth).

A particular set of nouns, describing things having two parts, comprises the major group of pluralia tantum in modern English:

glasses (a pair of spectacles), pants, panties, pantyhose, pliers, scissors, shorts, suspenders, tongs (metalworking & cooking), trousers, etc.

These words are interchangeable with a pair of scissors, a pair of trousers, and so forth. In the American fashion industry it is common to refer to a single pair of pants as a pant —though this is a back-formation, the English word (deriving from the French pantalon) was originally singular. In the same field, one half of a pair of scissors separated from the other half is, rather illogically, referred to as a half-scissor. Tweezers used to be part of this group, but tweezer has come into common usage only since the second half of the 20th century.

There are also some plural nouns whose singular forms exist, though they are much more rarely encountered than the plurals:

nuptial	nuptials
phalanx	phalanges
tiding	tidings
victual	victuals
viscus	viscera

Singulars without plurals

Mass nouns (or uncountable nouns) do not represent distinct objects, so the singular and plural semantics do not apply in the same way. Some examples:

• Abstract nouns

deceit, information, cunning, and nouns derived from adjectives, such as honesty, wisdom, beauty, intelligence, poverty, stupidity, curiosity, and words ending with “ness”, such as goodness, freshness, laziness, and nouns which are homonyms of adjectives with a similar meaning, such as good, bad (can also use goodness and badness), hot, and cold.

• In the arts and sciences

chemistry, geometry, surgery, the blues, jazz, rock and roll, impressionism, surrealism. This includes those that look plural but function as grammatically singular in English: mathematics (and in British English the shortened form ‘maths’), physics, mechanics, dynamics, statics, thermodynamics, aerodynamics, electronics, hydrodynamics, robotics, acoustics, optics, computer graphics, cryptography, ethics, linguistics, etc.; e.g., Mathematics is fun; Cryptography is the science of codes and ciphers; theromodynamics is the science of heat. Data often functions as a singular in terms such as ‘data collection’ or ‘data processing’.

• Chemical elements and other physical entities:

aluminum (US) / aluminium (UK), copper, gold, oxygen, nitrogen, carbon, equipment, furniture, traffic, air and water