To sack or to fire (5)
I believe the answer is:
rifle
I believe this is a double definition.
'to sack' is the first definition.
(both can mean to steal)
'to fire' is the second definition.
(thesaurus)
'or' acts as a link.
(Other definitions for rifle that I've seen before include "Go through in search" , "disarray" , "An arm" , "shoot?" , "Rummage" .)