Enormous bird eating a husband's fish (5)
I believe the answer is:
roach
'fish' is the definition.
(roach is a kind of fish)
'enormous bird eating a husband's' is the wordplay.
'enormous bird' becomes 'roc' (I've seen this before).
'eating' means one lot of letters goes inside another.
'husband' becomes 'h'.
'roc' placed around 'a' is 'roac'.
'roac'+'h'='ROACH'
(Other definitions for roach that I've seen before include "Small freshwater fish related to carp" , "Silver and red freshwater fish" , "Swimmer" , "Animal found in the water" , "Freshwatwer fish" .)