Female dog is fat (4)
I believe the answer is:
flab
'is fat' is the definition.
(I've seen this before)
'female dog' is the wordplay.
'female' becomes 'f' (abbreviation).
'dog' becomes 'lab' (short for labrador).
'f'+'lab'='FLAB'
(Other definitions for flab that I've seen before include "Ugly, surplus flesh" , "Sign of over-indulgence" , "Soft loose flesh" , "Loose body fat" , "Sign of overeating" .)