Spoken language (5)
I believe the answer is:
idiom
'spoken language' is the definition.
(idiom is a kind of spoken language)
This is the entire clue.
(Other definitions for idiom that I've seen before include "Colloquialism" , "Local style of expression" , "Group of words in which the meaning may not be obvious" , "Manner of speaking or writing" , "Characteristic style of expression" .)