Trunk fastener (4)
I believe the answer is:
hasp
'trunk fastener' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hasp that I've seen before include "Hinged fastening" , "Hinged fastener for door or lid" , "catch" , "part of a lock" , "Fastening plate, clasp" .)