Trap agreed following call (4)
I believe the answer is:
hook
'trap' is the definition.
(I've seen this before)
'agreed following call' is the wordplay.
'agreed' becomes 'ok' (eg when responding to an offer).
'following' says to put letters next to each other.
'call' becomes 'ho' (historical exclamation used to attract attention).
'ok' after 'ho' is 'HOOK'.
(Other definitions for hook that I've seen before include "Fixture for hanging" , "13's pirate chief" , "Bad golf shot" , "It's bent to catch or hold" , "Curved hanger; punch" .)