The Collaborative International Dictionary of English v.0.48:

Harlequin \Har"le*quin\ (h[aum]r"l[-e]*k[i^]n or -kw[i^]n), n.
   [F. arlequin, formerly written also harlequin (cf. It,
   arlecchino), prob. fr. OF. hierlekin, hellequin, goblin, elf,
   which is prob. of German or Dutch origin; cf. D. hel hell.
   Cf. Hell, Kin.]
   A buffoon, dressed in party-colored clothes, who plays
   tricks, often without speaking, to divert the bystanders or
   an audience; a merry-andrew; originally, a droll rogue of
   Italian comedy. --Percy Smith.
   [1913 Webster]

         As dumb harlequin is exhibited in our theaters.
                                                  --Johnson.
   [1913 Webster]

   Harlequin bat (Zool.), an Indian bat (Scotophilus
      ornatus), curiously variegated with white spots.

   Harlequin beetle (Zool.), a very large South American
      beetle (Acrocinus longimanus) having very long legs and
      antenn[ae]. The elytra are curiously marked with red,
      black, and gray.

   Harlequin cabbage bug. (Zool.) See Calicoback.

   Harlequin caterpillar. (Zool.), the larva of an American
      bombycid moth (Euch[ae]tes egle) which is covered with
      black, white, yellow, and orange tufts of hair.

   Harlequin duck (Zool.), a North American duck
      (Histrionicus histrionicus). The male is dark ash,
      curiously streaked with white.

   Harlequin moth. (Zool.) See Magpie Moth.

   Harlequin opal. See Opal.

   Harlequin snake (Zool.), See harlequin snake in the
      vocabulary.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

harlequin snake \har"le*quin snake`\ n.
   any of several venomous New World snakes brilliantly banded
   in red and black and either yellow or white, especially the
   eastern coral snake, a small poisonous snake (Micrurus
   fulvius or Elaps fulvius), ringed with red and black,
   found in the Southeastern United States. They are widely
   distributed in Southern and Central America;

   Syn: coral snake, New World coral snake.
        [WordNet 1.5]