Jouster's weapon (5)
I believe the answer is:
lance
'jouster's weapon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lance that I've seen before include "Spear carried by mounted soldier" , "Horseman's long weapon" , "Boy - prick (a boil)" , "Pierce (a boil)" , "Surgical knife" .)