Monsieur's mate (6)
I believe the answer is:
madame
'monsieur's mate' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for madame that I've seen before include "Flaubert novel" , "Married woman abroad" , "Proprietress of a brothel" , "A French-speaking woman" , "Frenchwoman's title" .)