Female performer's instrument (6)
I believe the answer is:
factor
'instrument' is the definition.
(thesaurus)
'female performer's' is the wordplay.
'female' becomes 'f' (abbreviation).
'performer' becomes 'actor' (actor is a kind of performer).
'f'+'actor'='FACTOR'
(Other definitions for factor that I've seen before include "Causal contribution to an outcome" , "Act for (anag)" , "Circumstance that contributes toward a result - arithmetically?" , "Seven is one for thirty five" , "Cause" .)