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.
a card other than a trump; plain card.
Origin of side card
An Americanism dating back to 1855–60
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019