Unusually clean weapon (5)
I believe the answer is:
lance
'weapon' is the definition.
(I know that lance is a type of weapon)
'unusually clean' is the wordplay.
'unusually' 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" , "Cut open" , "corporal may have at the front" , "Jousting weapon" , "Boy - prick (a boil)" .)