...smart celebrity holding back fantastic woman (7)
I believe the answer is:
electra
'fantastic woman' is the definition.
(mythical figure)
'smart celebrity holding back' is the wordplay.
'holding' says the answer is hidden in the clue.
'back' says the letters should be written backwards.
'artcele' can be found hidden inside 'smart celebrity'.
'artcele' backwards is 'ELECTRA'.
(Other definitions for electra that I've seen before include "Mourning Becomes ____ (play cycle Eugene O'Neill)" , "Female avenger" , "She sought vengeance" , "type of complex" , "Daughter of Agamemnon and Clytemnestra (who has a complex?)" .)