Woman in hidden identity (4)
I believe the answer is:
enid
'woman' is the definition.
(woman's name)
'in hidden identity' is the wordplay.
'in' says the answer is hidden in the clue.
'ENID' is hidden in the letters of 'hidden identity'.
(Other definitions for enid that I've seen before include "Writer of children's books, d. 1968" , "Dine with this girl" , "Lady" , "Miss Blyton" , "Arthurian wife" .)