The earliest use of the word 'rubber' to suggest a set of games or a deciding game - best of three, five etc - was in the 16th century and in reference to bowls rather than cards. I mean bowls, as played on grass rather than in a bowling-alley. Its first use in card-playing - whist, specifically - came nearly 200 years later. The actual origin of the word is obscure, according to The Oxford English Dictionary, but it appears to have nothing to do with 'rubber' as in 'rubber ball'.