The word Christmas is singular; the plural form is Christmases.
The plural form of Christmas is Christmases.
There is no plural form for the word, countries. This word itself is a plural.
The plural form of the word "inferno" is "infernos."
There is no plural word for if.
The plural form is data.
There is no 'plural form' of the word 'minute'. The word is both singular and plural.
The plural of diary is diaries.
The plural form of the word gelato is gelati.
The plural form of the word "baby" is "babies."
The plural form for the word 'pioneer' is pioneers.
The plural form of the word signal is signals.