Irregular Plural Nouns: Important Rules, Lists, and Examples

Last Updated on November 14, 2023

While most plural nouns follow a standard rule of adding an “s” or “es” to the end of the singular form, there are some irregular plural nouns that do not follow this pattern. These nouns often have unique spellings and can be challenging for language learners to master.

In this article, we will explore what irregular plural nouns are, how to form them, and provide examples to help you better understand their usage. We will also discuss common irregular plural noun patterns and provide tips for identifying and using them correctly. Let’s uncover the mysteries of irregular plural nouns together! 

What Are Irregular Plural Nouns?

Irregular Plural NounsPin

Irregular plural nouns are those that do not follow the standard rule of adding -s or -es to form their plural version. These nouns can be quite common in English, and they often require memorization to use correctly.

Irregular plural nouns don’t adhere to specific rules; therefore, it’s prudent to study them or search for accurate pluralization in the dictionary. Lack of definite rules makes it challenging to understand them. So, you must devote your time to study and memorize them. Otherwise, you’re bound to error when making use of irregular nouns in plural form.

Examples of irregular nouns in singular and plural format:

Singular Plural
Man Men
Foot Feet
Mouse Mice
Child Children
Woman Women
Goose Geese
Person People

Irregular Plural Nouns | Rules

No Change in the Plural

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

Irregular Plural Nouns List:

  • Aircraft – aircraft
  • Barracks – barracks
  • Deer – deer
  • Gallows – gallows
  • Moose – moose
  • Salmon – salmon
  • Hovercraft – hovercraft
  • Spacecraft – spacecraft
  • Series – series
  • Species – species
  • Means – means
  • Offspring – offspring
  • Deer – deer
  • Fish – fish
  • Sheep – sheep
  • Offspring – offspring
  • Trout – trout
  • Swine – swine

Changing the Spelling of the Singular Noun

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

Irregular Plural Nouns List:

  • Person – people
  • Ox – oxen
  • Man – men
  • Woman – women
  • Caveman – cavemen
  • Policeman – policemen
  • Child – children
  • Tooth – teeth
  • Foot – feet
  • Goose – geese
  • Mouse – mice
  • Louse – lice
  • Penny – pence

Note: There are many compounds of man and woman that form their plurals in the same way: postmen, policewomen, etc.

Irregular Plural Nouns from Latin and Greek

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

  • Alumna – alumnae
  • Formula – formulae/formulas
  • Antenna – antennae (for insects)/antennas (for electronic devices)

Final ex or ix becomes -ices

  • Index – indices /indexes
  • Matrix – matrices
  • Vertex – vertices
  • Appendix – appendices

Final is becomes es

  • Axis – axes
  • Genesis – geneses
  • Nemesis – nemeses
  • Crisis – crises
  • Testis – testes

Final um becomes -a, or just adds -s

Irregular Plural Nouns List:

  • Addendum – addenda
  • Corrigendum – corrigenda
  • Datum – data
  • Forum – fora/forums
  • Medium – media/ mediums
  • Memorandum – memoranda/memorandums
  • Millennium – millennia
  • Ovum – ova
  • Spectrum – spectra

Final us becomes -i or -era or -ora or just adds -es

Irregular Plural Nouns List:

  • Alumnus – alumni
  • Corpus – corpora
  • Census – censuses
  • Focus – foci
  • Genus – genera
  • Prospectus – prospectuses
  • Radius – radii
  • Campus – campuses
  • Succubus – succubi
  • Stylus – styli
  • Syllabus – syllabi/syllabuses
  • Viscus – viscera
  • Virus – viruses/virii
  • Cactus – cactuses/cacti
  • Fungus – fungi
  • Hippopotamus – hippopotamuses/hippopotami
  • Octopus – octopuses
  • Terminus – termini/terminuses
  • Uterus – uteri/uteruses

Final us remains unchanged in the plural

  • Meatus – meatus/meatuses
  • Status – status/statuses

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

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 Plural Nouns from Other Languages

Some nouns of French origin add an -x:

  • Beau – beaux/beaus
  • Bureau – bureaux/bureaus
  • Tableau – tableaux/tableaus

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
  • Matzah – matzot/matzahs
  • Kibbutz – kibbutzim/kibbutzes

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

  • Benshi – benshi
  • Otaku – otaku
  • Samurai – samurai

Nouns from languages other than the above generally form plurals as if they were native English words:

  • Canoe – canoes
  • Igloo – igloos
  • Kangaroo – kangaroos
  • Kayak – kayaks
  • Kindergarten – kindergartens
  • Pizza – pizzas
  • Sauna – saunas
  • Ninja – ninjas

Frequently Misused Irregular Plural Nouns

Irregular plural nouns are those that don’t follow the standard rule of adding -s or -es to form their plural versions. This can often lead to confusion and misuse in everyday writing and speech. This section will present a few widely misused irregular plural nouns and provide their correct plural forms.

Man / Men and Woman / Women: One common mistake is using mans or womans as plural forms, which is incorrect. The correct plurals are men and women.

Child / Children: Similarly, the plural of child is not childs but children.

Mouse / Mice and Goose / Geese: It’s essential to remember that the plural of mouse is mice, and the plural of goose is geese.

Tooth / Teeth and Foot / Feet: These nouns have plurals that are quite different from their singular forms. The correct plurals are teeth and feet, not tooths and foots.

Person / People: Though the irregular plural form is people, be aware that this does not apply to all cases. The word persons is used in legal contexts or specific situations involving a small number of individuals.

Here is a list of some other irregular plural nouns frequently misused:

Singular Correct Plural Incorrect Plural
Cactus Cacti Cactuses
Octopus Octopuses Octopi
Sheep Sheep Sheeps
Ox Oxen Oxes

Irregular Plural Nouns | Image 

Irregular Plural NounsPin

Irregular Plural Nouns Video

Learn more useful rules to form regular plural nouns in English.

Frequently Asked Questions

What are some common irregular plural nouns?

Irregular plural nouns are nouns that do not follow the typical rule of adding -s or -es to form their plural. Some common examples include:

  • Man -> Men
  • Woman -> Women
  • Child -> Children
  • Tooth -> Teeth
  • Foot -> Feet
  • Mouse -> Mice
  • Goose -> Geese
  • Cactus -> Cacti
  • Nucleus -> Nuclei
  • Datum -> Data

What are the rules for forming irregular plural nouns?

There is no single, universal rule for forming irregular plural nouns, but there are some tips and patterns that can help in learning them. For example:

  1. If the noun ends in -us, change the ending to -i (e.g., cactus -> cacti).
  2. If the noun ends in -f or -fe, change the ending to -ves (e.g., leaf -> leaves, wife -> wives).
  3. If the noun ends in -um or -on, change the ending to -a (e.g., bacterium -> bacteria, criterion -> criteria).

Keep in mind that these tips may not apply to every irregular plural noun and there are many exceptions.

Are there any patterns or categories for irregular plural nouns?

Although there are no strict rules for forming irregular plural nouns, some patterns can be observed. These patterns are often based on the origin of the word, such as Latin or Old English.

  1. Latin-derived words: Many irregular plurals are derived from Latin, with endings like -us turning into -i (e.g., cactus -> cacti), and -um into -a (e.g., bacterium -> bacteria).
  2. Old English words: Some irregular plural nouns come from Old English and have unique plural forms, such as man -> men, and tooth -> teeth.
  3. Same singular and plural forms: Some nouns have the same form in both singular and plural, like sheep and deer.

It’s important to note that these categories do not cover all instances, and some irregular plurals will not fit neatly into any of these patterns. Familiarity with the language and practice are the best ways to learn and understand irregular plural nouns.

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