Clean off weapon (5)
I believe the answer is:
lance
'weapon' is the definition.
(I know that lance is a type of weapon)
'clean off' is the wordplay.
'off' indicates an anagram.
'clean' anagrammed gives 'LANCE'.
(Other definitions for lance that I've seen before include "Knightly weapon" , "Long-shafted weapon" , "Surgical knife" , "Rider's long weapon" , "surgical instrument" .)