A mere game (4)
I believe the answer is:
pool
I believe this is a double definition.
'a mere' is the first definition.
(I've seen this before)
'game' is the second definition.
(pool is a kind of game)
(Other definitions for pool that I've seen before include "Puddle - game with balls" , "American game like snooker" , "Kitty; a billiard game" , "Ball game - small body of water" , "Put in common fund; (pub) game" .)