Female performers, experts concealing long hair (9)
I believe the answer is:
actresses
'female performers' is the definition.
(I've seen this before)
'experts concealing long hair' is the wordplay.
'experts' becomes 'aces' (ace is a kind of expert).
'concealing' indicates putting letters inside.
'long hair' becomes 'tress' (tress can mean a lock of hair).
'aces' enclosing 'tress' is 'ACTRESSES'.
(Other definitions for actresses that I've seen before include "they only pretend to work" , "Female impersonators" , "Stage performers" , "Female performers" , "Girls in play" .)