The Collaborative International Dictionary of English v.0.48:

Bird \Bird\ (b[~e]rd), n. [OE. brid, bred, bird, young bird,
   bird, AS. bridd young bird. [root]92.]
   1. Orig., a chicken; the young of a fowl; a young eaglet; a
      nestling; and hence, a feathered flying animal (see 2).
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            That ungentle gull, the cuckoo's bird. --Shak.
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            The brydds [birds] of the aier have nestes.
                                                  --Tyndale
                                                  (Matt. viii.
                                                  20).
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   2. (Zool.) A warm-blooded, feathered vertebrate provided with
      wings. See Aves.
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   3. Specifically, among sportsmen, a game bird.
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   4. Fig.: A girl; a maiden.
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            And by my word! the bonny bird
            In danger shall not tarry.            --Campbell.
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   Arabian bird, the phenix.

   Bird of Jove, the eagle.

   Bird of Juno, the peacock.

   Bird louse (Zool.), a wingless insect of the group
      Mallophaga, of which the genera and species are very
      numerous and mostly parasitic upon birds. -- Bird mite
      (Zool.), a small mite (genera Dermanyssus,
      Dermaleichus and allies) parasitic upon birds. The
      species are numerous.

   Bird of passage, a migratory bird.

   Bird spider (Zool.), a very large South American spider
      (Mygale avicularia). It is said sometimes to capture and
      kill small birds.

   Bird tick (Zool.), a dipterous insect parasitic upon birds
      (genus Ornithomyia, and allies), usually winged.
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WordNet (r) 3.0 (2006):

bird of passage
    n 1: someone who leads a wandering unsettled life [syn:
         wanderer, roamer, rover, bird of passage]
    2: any bird that migrates seasonally