flertall in English:

What’s the plural of “penny”?

The plural of word "key" is "keys".

What is the plural of 'leaf'?

'babies' is the plural of 'baby'

Trousers is a word that comes only in plural form.

Some English nouns have the same form in the singular and plural

With horse racing and such, these are called "stakes". For this meaning the plural form is often used.

The plural form of "louse" is "lice".

The plural form of 'person' is 'people', not 'persons'.

In Esperanto an adjective ends in "a." The plural is formed by adding "j."

What is the plural of Nazi? - "Assholes."