The old-fashioned DA, say? (7)
I believe the answer is:
haircut
'the old-fashioned da say?' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
This is the entire clue.
Can you help me to learn more?
(Other definitions for haircut that I've seen before include "Crop possibly" , "Style of coiffure" , "Bob possibly" , "Mohican, possibly" , "shock treatment" .)