Weapon sometimes placed in front of corporal (5)
I believe the answer is:
lance
'corporal' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for lance that I've seen before include "Weapon of knights of old" , "Cut open" , "Incise" , "Long weapon; prick" , "Old cavalry weapon" .)