Madam's counterpart (3)
I believe the answer is:
sir
'madam's counterpart' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sir that I've seen before include "Knight's prefix" , "Feted fellow" , "Formal term of address" , "Honourable title" , "Term of address for a gentleman" .)