Wiktionary Appendix:Irregular plurals

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. Compound words that
6. Words from Latin that end in -a change -a to -ae (eg, formula becomes formulae in the mathematical and chemical senses)
7. Words from Latin that end in -ex change -ex to -ices (eg, vortex becomes vortices)
8. Words that end in -f or -fe change -f or -fe to -ves (eg, calf becomes calves; knife becomes knives)
9. Words that end in -ful that add an s either before or after the s (eg, spoonful becomes either spoonsful or spoonfuls)
10. Words from Latin that end in -is change -is to -es (eg, thesis becomes theses)
11. Words from Latin that end in -ix change -ix to -ices (eg, matrix becomes matrices)
12. Words from Greek that end in -ma change -ma to -mata (eg, stigma becomes stigmata in all senses but the sense of "disgrace")
13. Words from Latin that end in -nx change -nx to -nges (eg, meninx becomes meninges)
14. Words from Greek that end in -on change -on to -a (eg, polyhedron becomes polyhedra)
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)
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)
20. Words that end in -s or -ese denoting a national of a particular country (eg, Swiss and Chinese)

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.

Singluar	Plural	Notes
child	children	Also for nouns ending in -child in the sense of a particular type of child, such as schoolchild
die	dice	in the sense of a numbered cube used in games; dice is often also used as the singular
foot	feet	The plural foot is used colloquially in the sense of the unit of distance
goose	geese	The plural of mongoose is mongooses
louse	lice	Also for the names of animals ending in -louse, such as woodlouse, which becomes woodlice
man	men	Also for nouns ending in -man in the sense of a particular type of man, such as postman or Frenchman; words ending in -man that have another origin are regular (eg, ataman becomes atamans; shaman becomes shamans)
mouse	mice	Also applies to the names of other animals that end in -mouse, such as dormouse and titmouse, which become dormice and titmice respectively; the plural mouses is sometimes used for the computer peripheral
ox	oxen	Also applies to the names of other animals that end in ox, such as musk-ox
penny	pence	Also for multiples of a penny, such as sixpence. Pence is used only the sense of an amount of money; in the sense of a number of coins worth a penny each, the plural is pennies
person	people	Also for nouns ending in -person, such as chairperson, which becomes chairpeople. In formal contexts, the plural is persons (and similarly for nouns ending in -person); people is also a singular noun in the sense of a community of people
tooth	teeth	Also for nouns ending in -tooth, such as eyetooth, which becomes eyeteeth
woman	women	Also for nouns ending in -woman in the sense of a particular type of woman, such as policewoman or Englishwoman

See also