It's on the hook (4)
I believe the answer is:
bait
'it's on the hook' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bait that I've seen before include "What lures" , "Food to entice fish; taunt" , "Tempt" , "Allurement" , "Enticement for fish" .)