A weapon in playing billiards (6)
I believe the answer is:
cannon
This could be a double definition.
'a weapon' is the first definition.
(cannon is a kind of weapon)
'playing billiards' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'in' acts as a link.
Can you help me to learn more?
(Other definitions for cannon that I've seen before include "Large wheeled gun" , "Large artillery piece" , "Caught girl on piece of artillery" , "Large gun mounted on wheels" , "Heavy ordnance" .)