Английский Этимологический словарь - deck (n.)

- 1466, probably aphetic of M.L.G. verdeck, a nautical word, from ver- "fore" + decken "to cover, put under roof," from P.Gmc. *thackjam. Sense extended early in Eng. from "covering" to "platform of a ship." "Pack of cards" is c.1593, perhaps because they were stacked like decks of a ship. The verb sense of "knock down" is first recorded c.1953, probably from notion of laying someone out on the deck.