The Collaborative International Dictionary of English v.0.48:

Robin \Rob"in\, n. [Properly a pet name for Robert, originally
   meaning, famebright; F., fron OHG. Roudperht; ruod (in comp.;
   akin to AS. hr?? glory, fame, Goth. hr?peigs victorius) +
   beraht bright. See Bright, Hob a clown.] (Zool.)
   (a) A small European singing bird (Erythacus rubecula),
       having a reddish breast; -- called also robin
       redbreast, robinet, and ruddock.
   (b) An American singing bird (Merula migratoria), having
       the breast chestnut, or dull red. The upper parts are
       olive-gray, the head and tail blackish. Called also
       robin redbreast, and migratory thrush.
   (c) Any one of several species of Australian warblers of the
       genera Petroica, Melanadrays, and allied genera; as,
       the scarlet-breasted robin (Petroica mullticolor).
   (d) Any one of several Asiatic birds; as, the Indian robins.
       See Indian robin, below.
       [1913 Webster]

   Beach robin (Zool.), the robin snipe, or knot. See Knot.


   Blue-throated robin. (Zool.) See Bluethroat.

   Canada robin (Zool.), the cedar bird.

   Golden robin (Zool.), the Baltimore oriole.

   Ground robin (Zool.), the chewink.

   Indian robin (Zool.), any one of several species of Asiatic
      saxoline birds of the genera Thamnobia and Pratincola.
      They are mostly black, usually with some white on the
      wings.

   Magrie robin (Zool.), an Asiatic singing bird (Corsycus
      saularis), having the back, head, neck, and breast black
      glossed with blue, the wings black, and the belly white.


   Ragged robin. (Bot.) See under Ragged.

   Robin accentor (Zool.), a small Asiatic singing bird
      (Accentor rubeculoides), somewhat resembling the
      European robin.

   Robin redbreast. (Zool.)
   (a) The European robin.
   (b) The American robin.
   (c) The American bluebird.

   Robin snipe. (Zool.)
   (a) The red-breasted snipe, or dowitcher.
   (b) The red-breasted sandpiper, or knot.

   Robin's plantain. (Bot.) See under Plantain.

   Sea robin. (Zool.)
   (a) Any one of several species of American gurnards of the
       genus Prionotus. They are excellent food fishes. Called
       also wingfish. The name is also applied to a European
       gurnard.
   (b) The red-breasted merganser, or sheldrake. [Local, U.S.]


   Water robin (Zool.), a redstart (Ruticulla fuliginosa),
      native of India.
      [1913 Webster]

WordNet (r) 3.0 (2006):

robin
    n 1: small Old World songbird with a reddish breast [syn:
         robin, redbreast, robin redbreast, Old World robin,
         Erithacus rubecola]
    2: large American thrush having a rust-red breast and abdomen
       [syn: robin, American robin, Turdus migratorius]