Look nothing but a game (3)
I believe the answer is:
loo
'a game' is the definition.
(historical card game)
'look nothing' is the wordplay.
'look' becomes 'lo' (archaic exclamation meaning 'look!').
'nothing' becomes 'O' (looks like zero - 0).
'lo'+'o'='LOO'
'but' acts as a link.
(Other definitions for loo that I've seen before include "Rest room" , "A colloquial toilet" , "Ladies, perhaps" , "Privy" , "Toilet (informal)" .)