Daughter gets terribly fat and stupid (4)
I believe the answer is:
daft
'stupid' is the definition.
(I've seen this before)
'daughter gets terribly fat' is the wordplay.
'daughter' becomes 'd'.
'gets' means one lot of letters go next to another.
'terribly' indicates anagramming the letters.
'fat' anagrammed gives 'aft'.
'd'+'aft'='DAFT'
'and' acts as a link.
(Other definitions for daft that I've seen before include "'---- as a brush': dotty" , "Informally silly or crazy" , "Idiotic" , "Informally silly or foolish" , "Potty" .)