1590s, "throw out or reject a card dealt to a player, in accordance with the rules of the game," literally "to throw a card away," from dis- "away" + card (n.1). Figurative use (in a non-gaming sense) "cast off, dismiss" is attested slightly earlier (1580s). In the card-playing sense, decard is attested by 1550s. Related: Discarded; discarding. As a noun, "act of discarding or rejecting," from 1742.