Idiom or vernacular (7)
I believe the answer is:
I believe this clue is a double definition.
'idiom' is the first definition.
(I know that idiom can be written as dialect)
'vernacular' is the second definition.
(I've seen this before)
(Other definitions for dialect that I've seen before include "Regional form of speech" , "Local speech variant" , "talk from the regions" , "Regional language form" , "Local language variant" .)