Daughter taken in by lad's physique (4)
I believe the answer is:
body
'physique' is the definition.
(I've seen this before)
'daughter taken in by lad's' is the wordplay.
'daughter' becomes 'd'.
'taken in by' means one lot of letters goes inside another.
'lad' becomes 'boy' (I've seen this before).
'd' placed into 'boy' is 'BODY'.
(Other definitions for body that I've seen before include "Carcase" , "Physical structure of an organism" , "Corpus" , "Stiff" , "Substance" .)