Inducement of sex rejected in advance (6)
I believe the answer is:
motive
'inducement' is the definition.
(I've seen this in another clue)
'sex rejected in advance' is the wordplay.
'sex' becomes 'it' (a common euphemism).
'rejected' is a reversal indicator.
'in' indicates putting letters inside.
'advance' becomes 'move'.
'it' reversed gives 'ti'.
'ti' put inside 'move' is 'MOTIVE'.
'of' acts as a link.
(Other definitions for motive that I've seen before include "Underlying purpose" , "Reason for doing something, perhaps a crime" , "What induces one to take a certain action" , "Reason for doing something, say murder" , "Purpose - reason" .)