Club bum? (8)
I believe the answer is:
bludgeon
This clue could be a double definition.
'club' is the first definition.
(both can mean a heavy weapon)
'bum?' is the second definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
Can you help me to learn more?
(Other definitions for bludgeon that I've seen before include "Short stick with thickened end as weapon" , "Thick stick as weapon" , "Club used as a weapon" , "Bully; heavy weapon" , "Thick club" .)