Corpulent, that woman's dad (6)
I believe the answer is:
father
'dad' is the definition.
(I've seen this before)
'corpulent that woman's' is the wordplay.
'corpulent' becomes 'fat' ('fat' can be similar in meaning to 'corpulent').
'that woman' becomes 'her' (I've seen this before**).
'fat'+'her'='FATHER'
(Other definitions for father that I've seen before include "dad" , "pops" , "So-called priest" , "Patriarch" , "Old man" .)