Female is not dim (5)
I believe the answer is:
faint
'dim' is the definition.
(I know that dim can be written as faint)
'female is not' is the wordplay.
'female' becomes 'f' (abbreviation).
'is not' becomes 'aint' ('ain't' is a non-standard form of 'isn't').
'f'+'aint'='FAINT'
(Other definitions for faint that I've seen before include "Lacking clarity" , "(Of a chance) slight" , "dull" , "Swoon, pass out" , "Swoon; indistinct" .)