Hear; fastener (5)
I believe the answer is:
catch
I believe this clue is a double definition.
'hear' is the first definition.
(catching is a kind of hearing)
'fastener' is the second definition.
(I know that catch is a type of fastener)
(Other definitions for catch that I've seen before include "Understand" , "Grasp - overtake - overhear - surprise" , "problem being concealed" , "Drawback that's not immediately evident" , "Grab hold of - fastener" .)