The Collaborative International Dictionary of English v.0.48:

Decoy \De*coy"\, n.
   1. Anything intended to lead into a snare; a lure that
      deceives and misleads into danger, or into the power of an
      enemy; a bait.
      [1913 Webster]

   2. A fowl, or the likeness of one, used by sportsmen to
      entice other fowl into a net or within shot.
      [1913 Webster]

   3. A place into which wild fowl, esp. ducks, are enticed in
      order to take or shoot them.
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   4. A person employed by officers of justice, or parties
      exposed to injury, to induce a suspected person to commit
      an offense under circumstances that will lead to his
      detection.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decoy \De*coy"\ (d[-e]*koi"), v. t. [imp. & p. p. Decoyed
   (-koid"); p. pr. & vb. n. Decoying.] [Pref. de- + coy;
   orig., to quiet, soothe, caress, entice. See Coy.]
   To lead into danger by artifice; to lure into a net or snare;
   to entrap; to insnare; to allure; to entice; as, to decoy
   troops into an ambush; to decoy ducks into a net.
   [1913 Webster]

         Did to a lonely cot his steps decoy.     --Thomson.
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         E'en while fashion's brightest arts decoy,
         The heart, distrusting, asks if this be joy.
                                                  --Goldsmith.

   Syn: To entice; tempt; allure; lure. See Allure.
        [1913 Webster]

WordNet (r) 3.0 (2006):

decoy
    n 1: a beguiler who leads someone into danger (usually as part
         of a plot) [syn: decoy, steerer]
    2: something used to lure fish or other animals into danger so
       they can be trapped or killed [syn: bait, decoy, lure]
    v 1: lure or entrap with or as if with a decoy