Wrong, a girl (5)
I believe the answer is:
amiss
'wrong' is the definition.
('amiss' can be a synonym of 'wrong')
'a girl' is the wordplay.
'girl' becomes 'miss' (I've seen this before**).
'a'+'miss'='AMISS'
(Other definitions for amiss that I've seen before include "Wrorg" , "Faulty" , "Fallacious" , "Not quite right" , "Not functioning properly" .)