Les mots se terminant en "-y" prendront généralement la terminaison "-ies" :

party --> parties

Certains mots sont irréguliers au pluriel :

one man --> two men

one woman --> two women

one person --> two people

one foot --> two feet

one mouse --> two mice

one goose --> two geese

one tooth --> two teeth

one wife --> two wives

one child --> two children

one knife --> two knives

one thief --> two thieves

one dwarf --> two dwarves (ou: dwarfs)

one potato --> two potatoes

one leaf --> two leaves

one life --> two lives

one loaf --> two loaves

one half --> two halves

Certains mots rarissimes ne changent pas du tout au pluriel :

one moose --> two moose

one sheep --> two sheep

one aircraft --> two aircraft

Les mots d'origine latine ou grecque qui ont retenu une terminaison antique se conformeront généralement à la forme plurielle de leur langue d'emprunt :

one alumnus --> two alumni

one syllabus --> two syllabi

one alumna --> two alumnae

one alga --> many algae

one forum --> many fora (ou : forums)

one thesis --> two theses

one hypothesis --> two hypotheses

one phenomenon --> two phenomena

one cactus --> two cacti (ou : cactuses)

one diagnosis --> two diagnoses

one oasis --> two oases