mid-15c., probably aphetic of M.L.G. verdeck, a nautical word, from ver- "fore" + decken "to cover, put under roof," from P.Gmc. *thackjam (related to thatch), from PIE *(s)tog-/*(s)teg- "cover" (see stegosaurus). Sense extended early in
English from "covering" to "platform of a ship." "Pack of cards" is 1590s, 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. Deck chair (1884) so called because they were used on ocean liners. Tape deck (1949) is in ref. to the flat surface of old reel-to-reel tape recorders.
"adorn" (as in deck the halls), c.1500, from M.Du. dekken "to cover," from the same P.Gmc. root as deck (n.). Replaced O.E. þeccan.