Common phrase (5)
I believe the answer is:
idiom
'common phrase' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for idiom that I've seen before include "Language peculiar to a particular group" , "Form or variety of language" , "particular phrase" , "Language used by people or group, vernacular" , "Dialect, vernacular" .)