ox oxen (particularly when referring to a team of draft animals, sometimes oxes in nonstandard American English)
child children (actually earlier plural "cildra/cildru" plus -en suffix, forming a double plural)
brother brethren (archaic plural of brother; earlier "brether" plus -en suffix, forming a double plural; now used in fraternal order)
cow kine (archaic/regional; actually earlier plural "kye" [cf. Scots "kye" - "cows"] plus -en suffix, forming a double plural)
D: variants of -en.
No plural difference:
The plural is sometimes formed by simply changing the vowel sound of the singular, in a process called ablaut (these are sometimes called mutated plurals):
Greek and Latin derived:
* Final a becomes -ae (also -æ), or just adds -s:
* Final ex or ix becomes -ices (pronounced /ɨsiːz/), or just adds -es:
index indices /ˈɪndɨsiːz/ or indexes
* Final is becomes es (pronounced /iːz/):
axis axes /ˈæksiːz/
* Final ies remains unchanged:
* Final on becomes -a:
* Final um becomes -a, or just adds -s:
* Final us becomes -i (second declension, [aɪ]) or -era or -ora (third declension), or just adds -es (especially in fourth declension, where it would otherwise be the same as the singular):
* Final as in one case of a noun of Greek origin changes to -antes:
Atlas Atlantes (statues of the hero); but
* Some nouns of French origin add an -x, which may be silent or pronounced /z/:
* Nouns of Hebrew origin add -im or -ot (generally m/f) according to native rules, or just -s:
Words better known in the plural
Some words of foreign origin are much better known in the plural; usage of the original singular may be considered pedantic or actually incorrect or worse by some speakers. In common usage, the original plural is considered the singular form. In many cases, back-formation has produced a regularized plural.
Original singular Original plural/
common singular Common plural
agendum agenda9 agendas
alga algae algae
biscotto biscotti biscotti
candelabrum candelabra candelabras
datum10 data data (mass noun)
graffito graffiti graffiti (mass noun)
insigne insignia insignias
opus opera operas
panino panini paninis (currently gaining use)
paparazzo paparazzi paparazzi
spaghetto spaghetti spaghetti
D - having fun yet?
Chinese 'xie' for plural (some) seems nice.
But then they have special words for plurals of many many singular words.
In English, herd of cattle et al.