Female, not in dresses, stuns (5)
I believe the answer is:
rocks
'stuns' is the definition.
'female not in dresses' is the wordplay.
'female' becomes 'f' (common abbreviation).
'not in' is a deletion indicator.
'dresses' becomes 'frocks' (frocking is a kind of dressing).
'frocks' with 'f' taken out is 'ROCKS'.
(Other definitions for rocks that I've seen before include "Sways; stuns" , "cocaine?" , "Regular moves to get child off" , "Shakes violently - perhaps to mod music" , "Large stones" .)