Occasionally gluing piece (3)
I believe the answer is:
gun
'piece' is the definition.
(slang term for a gun)
'occasionally gluing' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternating letters of 'gluing' are 'GUN'.
(Other definitions for gun that I've seen before include "Arm" , "Throttle" , "Firearm" , "An offensive weapon" , "It can be carried by 15 Ac" .)