Creature wife caught in trap (4)
I believe the answer is:
newt
'creature' is the definition.
(newt is a kind of creature)
'wife caught in trap' is the wordplay.
'wife' becomes 'w'.
'caught in' means one lot of letters goes inside another.
'trap' becomes 'net' (net is a kind of trap**).
'w' put inside 'net' is 'NEWT'.
(Other definitions for newt that I've seen before include "Amphibious salamander" , "Ask" , "Went (anag.)" , "Small tailed amphibian" , "Pond creature" .)