Clean adapted weapon (5)
I believe the answer is:
lance
'weapon' is the definition.
(lance is a kind of weapon)
'clean adapted' is the wordplay.
'adapted' indicates anagramming the letters.
'clean' is an anagram of 'LANCE'.
(Other definitions for lance that I've seen before include "Spear for a horse-soldier" , "Shafted weapon used on horseback" , "Knightly weapon" , "Weapon of knights of old" , "Old cavalry weapon" .)