Clean off a weapon (5)
I believe the answer is:
lance
'a weapon' is the definition.
(lance is a kind of weapon)
'clean off' is the wordplay.
'off' indicates anagramming the letters.
'clean' with letters rearranged gives 'LANCE'.
(Other definitions for lance that I've seen before include "Long pointed weapon of old" , "Spear for a horse-soldier" , "Pierce (a boil)" , "Long-shafted weapon" , "Chap" .)