Opera for automobile workers? (6)
I believe the answer is:
'opera' is the definition.
(I've seen this before)
'automobile workers?' is the wordplay.
'automobile' becomes 'car' (synonyms).
'workers?' becomes 'men' (man is a kind of worker).
'for' acts as a link.
(Other definitions for carmen that I've seen before include "Musical from Bizet opera" , "Bizet's great Spanish opera" , "Spanish opera by Bizet" .)