Catch husband out — is one listening? (3)
I believe the answer is:
ear
'is one listening?' is the definition.
(an ear is something which listens)
'catch husband out' is the wordplay.
'catch' becomes 'hear' (to catch something is to hear it being spoken).
'husband' becomes 'h'.
'out' indicates named letters should be taken away.
'hear' with 'h' taken out is 'EAR'.
(Other definitions for ear that I've seen before include "Place for a plug" , "Spike of, eg, corn" , "Organ inside heart" , "Hearing aid?" , "Part of corn plant" .)