irregular plural

In English grammar, an irregular plural noun is a noun that forms its plural in a way other than by adding "-s" or "-es". This often reflects older methods of pluralization.12

Examples of irregular plurals include:
* Nouns that change vowel sounds, such as foot to feet, or mouse to mice.2
* Nouns that add "-en," like child to children or ox to oxen.2
* Nouns that remain the same in both singular and plural forms, such as moose or sheep.2
* Loanwords from languages like Latin or Greek that retain their original plural forms, such as datum becoming data or phenomenon becoming phenomena.2