Pocket billiards (4)
I believe the answer is:
pool
'pocket billiards' is the definition.
(synonyms)
This is all the clue.
(Other definitions for pool that I've seen before include "Small body of still water" , "Kitty; a billiard game" , "Reserve" , "Lido - kitty - ball game" , "Organization of people or resources that can be shared" .)