Damsel fails to conceal identity (4)
I believe the answer is:
self
'identity' is the definition.
(I've seen this in another clue)
'damsel fails to conceal' is the wordplay.
'to conceal' indicates the answer is hidden within the clue.
'SELF' can be found hidden inside 'damsel fails'.
(Other definitions for self that I've seen before include "A person's awareness of their own identity" , "One's individuality" , "Personality" , "Will perhaps" , "Will the author" .)