The word prolix is used solely as an adjective, and as such does not have a plural form.
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 anagram is the word prolix.
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.
The plural form of the word 'deed' is 'deeds'.