Catch sight of in wife's pyjamas (4)
I believe the answer is:
espy
'catch sight of' is the definition.
(espying is a kind of catching sight of)
'in wife's pyjamas' is the wordplay.
'in' says the answer is hidden in the clue.
'ESPY' is hidden in the letters of 'wifes pyjamas'.
(Other definitions for espy that I've seen before include "Detect" , "Spot at a distance" , "Observe, notice" , "Behold" , "Spot, notice" .)