Appendix:English irregular nouns

The table below lists English words that have irregular plurals.

Rules
Not included are words that follow any of the following rules:


 * 1) Words that add -s, which are regular plurals
 * 2) Words that end in -ch, -o, -s, -sh, -x, -z
 * 3) Symbols or letters, which often add -'s
 * 4) Words that are invariant in the plural (eg, deer, series)
 * 5) Words from Latin that end in -a change -a to -ae (eg, formula becomes formulae in the mathematical and chemical senses)
 * 6) Words from Latin that end in -ex change -ex to -ices (eg, vortex becomes vortices)
 * 7) Words that end in -f or -fe change -f or -fe to -ves (eg, calf becomes calves; knife becomes knives)
 * 8) Words that end in -ful that add an s after the -ful (eg, spoonful becomes spoonfuls; note that spoonsful is incorrect)
 * 9) Words from Latin that end in -is change -is to -es (eg, thesis becomes theses)
 * 10) Words from Latin that end in -ix change -ix to -ices (eg, matrix becomes matrices)
 * 11) Words from Greek that end in -ma change -ma to -mata (eg, stigma becomes stigmata in all senses but the sense of "disgrace")
 * 12) Words from Latin that end in -nx change -nx to -nges (eg, meninx becomes meninges)
 * 13) Words from Greek that end in -on change -on to -a (eg, polyhedron becomes polyhedra)
 * 14) Words that end in -s or -ese denoting a national of a particular country (eg, Swiss and Chinese)
 * 15) Words from French that end in -u add an x (eg, château becomes châteaux)
 * 16) Words from Latin that end in -um change -um to -a (eg, minimum becomes minima)
 * 17) Words from Latin that end in -us change -us to -i or -era (eg, radius becomes radii; genus becomes genera; but note octopus is different)
 * 18) Words that end in -y preceded by a consonant change -y to -ies (eg, baby becomes babies)
 * 19) Words from Hebrew that add -im or -ot (eg, cherub becomes cherubim)

Source: Wikipedia article on English plurals, which you can see for much more information.

'''Some of words of foreign origin that have the endings above can form or always form their plurals regularly. The list above should therefore be considered as a guide only. See particular words to determine their plurals.'''

Umlaut
The following plurals exhibit umlaut, meaning that they are inflected by changing the vowel, as in man/men. These stem from the stem vowel being mutated due to a following /i/ contained in Germanic consonant stem plurals that later vanished.

Weak noun
The following plurals are relics of Old English weak noun inflection, where the plural was formed by suffixing -an/-ena/-um, depending on case, which yields the ending.

“oxen” is ox-en, while “children” is in fact a double plural: “cild-ru-en”, where -ru is a strong noun plural, and -en is a weak noun plural.

and are humorous computing slang formed by the same rule.

Suppletive
A suppletive plural is a plural whose root is different from the root of the singular, i.e., not from the same underlying word.

Devoiced regular plural endings
“pence” is a contraction of “pennies”, collective plural of “penny”.