Dead ringers and French ladies' wear (4-3)
I believe the answer is:
twin-set
'ladies' wear' is the definition.
The definition suggests a singular noun which matches the answer.
'dead ringers and french' is the wordplay.
'dead ringers' becomes 'twins' (I am not sure about this - if you are sure you should believe this answer much more).
'and french' becomes 'et' ('and' in French).
'twins'+'et'='TWIN-SET'
Can you help me to learn more?
(Other definitions for twin-set that I've seen before include "Wear associated with pearls?" , "Two-piece outfit" , "Matching garments" , "Matching cardigan and jumper worn together" .)