Informal words in various languages (5)
I believe the answer is:
slang
'informal words' is the definition.
(I've seen this in another clue)
'in various languages' is the wordplay.
'in' indicates a hidden word.
'SLANG' can be found hidden inside 'various languages'.
(Other definitions for slang that I've seen before include "Informal speech" , "Informal language - jargon" , "abuse" , "See 15" , "Patois" .)