Ox becomes Oxen when plural.
Some nouns ending in -en are:alienamenbeenburdenchildrencanteenchickendendozenelevenevenflaxenfrozengardenglenheavenhenibuprofenkeenkitchenlinenlistenmenmittennitrogenomenoxenpenprovenqueenravenrottenseenseventeenthenvelveteenvixenwhenwomenyenZen
there is no plural for "en", even when all the other words are plural in the phrase: je suis en chemise - I am in shirt. ils sont en chaussures - they are in shoes
The word ox is derived from the Old English oxa, the plural of which was oxan. Over time oxa became ox and oxan became oxen.
"Children" has two old plural signs, both the r and the n. Other old words retaining the plural in -en are oxen and brethren. The plurals men and women are not formed the same way, however. In their case, it is the vowel that changes to create the plural, not the addition of -en.
In English, almost all nouns form their plural form by adding -s to the singular form (book > books). A handful of these, ending in -f, change the -f to a -v as well (calf > calves).Exactly seven English nouns form the plural by changing a vowel:foot > feetgoose > geeselouse > liceman > menmouse > micetooth > teethwoman > womenAnd three add -en instead of -s:brother > brethren (archaic form, no longer used)child > childrenox > oxenA number of nouns that refer to animals have no distinct plural form at all:deer > deerfish > fishmoose > moosequail > quail(etc.)Then there are a number of nouns borrowed from Latin or Greek, whose plurals in English are the same as in their original language:(from Latin):appendix > appendicesgenus > generaradius > radii...etc.(from Greek):analysis > analysesphenomenon > phenomena...etc.[source: Pinker, Words and Rules]
Unlike regular English nouns that form the plural by adding 's' or 'es' to the end of the word, irregular English nouns require vowel or consonant changes, or suffixation. For some common nouns of Old English origin, the vowel undergoes a change (ablaut). For example:foot > feetman > menwoman > womenmouse > micetooth > teethSome other common nouns of Old English origin require the addition of 'n' or 'en' to form the plural. For example:child > childrenox > oxenYet other common nouns, which are often of Old English origin and refer to groups of animals, have identical plural and singular form. For example:deer > deermoose > moosetrout > troutoffspring > offspringsheep > sheepFor nouns of Latin origin that end in an 'a', change the 'a' to 'ae' to form the plural. For example:formula > formulaealumna > alumnaeFor nouns of Latin origin that end in 'ex' or 'ix', change the suffix to 'ices'. For example:matrix > matricesvertex > verticesindex > indicesFor nouns of Latin origin that end in 'is', change the 'is' to 'es'. For example:axis > axescrisis > crisesanalysis > analysesthesis > thesesFor nouns of Latin origin that end in 'on', change 'on' to 'a'. For example:criterion > criteriaphenomenon > phenomenaautomaton > automataFor nouns of Latin origin that end in 'um', change 'um' to 'a'. For example:datum > datamedium > mediaaddendum > addendamillennium > millenniaFor nouns of Latin origin that end in 'us', change the 'us' to 'i', 'era', 'ora' or 'es'. For example:syllabus > syllabigenus > generacorpus > corporacensus > censusesFor nouns of Greek origin that end in 'ma', add 'ta' to the end of the word to form the plural. For example:dogma > dogmatastigma > stigmataschema > schemataFor nouns of French origin that end in 'eau', add 'x' to the end of the word to form the plural. For example:chateau > chateauxbeau > beauxbureau > bureauxFor nouns of Hebrew origin, add 'im' or 'ot' to the end of the word to form the plural. For example:cherub > cherubimmatzah > matzot
¿Está usted en el autobús? (singular, formal) ¿Estás en el autobús? (singular, informal) ¿Están en el autobús? (plural, formal) Estais en el autobus? (plural, informal)
l'arc-en-ciel, plural: des arcs-en-ciel.
Some examples of irregular plurals are:man, menperson, peoplegoose, geesebasis, basesoasis, oasesfoot, feettooth, teethmouse, micecrisis, crisesemphasis, emphases
The en passant rule was added to chess in the 15th century.
'en vacances' (always plural)
No hay acento en la forma plural de palabras que terminan en 'ción'. There is no accent mark in the plural form of words that end in 'ción"