Weapon held up by a corporal? (5)
I believe the answer is:
lance
I believe this clue is a double definition.
'weapon held up' is the first definition.
'a corporal?' is the second definition.
(thesaurus)
'by' is the link.
(Other definitions for lance that I've seen before include "surgical instrument" , "Weapon of knights of old" , "Long-shafted weapon" , "Knightly weapon" , "Spear carried by mounted soldier" .)