It's a trap! (4)
I believe the answer is:
bait
'it's a trap' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for bait that I've seen before include "Set a trap with food" , "Food to entice fish; taunt" , "Angler's lure for fish" , "Food on a hook to attract fish" , "Enticement for fish" .)