Favour topless partner (6)
I believe the answer is:
spouse
'partner' is the definition.
('spouse' can be a synonym of 'partner')
'favour topless' is the wordplay.
'favour' becomes 'espouse'.
'topless' means to remove the first letter.
'espouse' with its first letter taken off is 'SPOUSE'.
(Other definitions for spouse that I've seen before include "Other half" , "old lady?" , "Married partner" , "Partner in marriage" , "Consort" .)