What is an irrgular noun?

A regular plural is a noun to which an -s or an -es is added to the end of the Word to form the plural.
An irregular plural noun is a plural formed in some other way.

Examples of irregular plural nouns:

singular / plural

• alumnus / alumni
• baby / babies
• bacterium / bacteria
• cactus / cacti
• child / children
• foot / feet
• goose / geese
• knife / knives
• man / men
• medium / media
• memory / memories
• mouse / mice
• ox / oxen
• person / people
• tooth / teeth
• wife / wives
• woman / women