side card

noun

, Cards.

1. Poker. the highest card in a hand that is not part of a scoring combination, as not being one of a pair, three of a kind, etc., and that serves to determine by its denomination the higher ranking of two otherwise equal hands.
2. a card other than a trump; plain card.

Word History and Origins

Origin of side card¹

An Americanism dating back to 1855–60