Diamond; game (9)
I believe the answer is:
solitaire
I believe this is a double definition.
'diamond' is the first definition.
(solitaire is a type of diamond)
'game' is the second definition.
(I know that solitaire is a type of card game)
(Other definitions for solitaire that I've seen before include "Single stone in jewellery" , "Game for one person - single gem" , "game > bird" , "Patience of Americans" , "recluse" .)