Clean off a weapon (5)
I believe the answer is:
lance
'a weapon' is the definition.
(I know that lance is a type of weapon)
'clean off' is the wordplay.
'off' indicates an anagram.
'clean' is an anagram of '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" .)