The Collaborative International Dictionary of English v.0.48:

ostrich \os"trich\ ([o^]s"trich), n. [OE. ostriche, ostrice, OF.
   ostruche, ostruce, F. autruche, L. avis struthio; avis bird +
   struthio ostrich, fr. Gr. ?, fr. ? bird, sparrow. Cf.
   Aviary, Struthious.] [Formerly written also estrich.]
   (Zool.)
   A large bird of the genus Struthio, of which Struthio
   camelus of Africa is the best known species. It has long and
   very strong legs, adapted for rapid running; only two toes; a
   long neck, nearly bare of feathers; and short wings incapable
   of flight. The adult male is about eight feet high.
   [1913 Webster]

   Note: The South African ostrich (Struthio australis) and
         the Asiatic ostrich are considered distinct species by
         some authors. Ostriches are now domesticated in South
         Africa in large numbers for the sake of their plumes.
         The body of the male is covered with elegant black
         plumose feathers, while the wings and tail furnish the
         most valuable white plumes.
         [1913 Webster]

   Ostrich farm, a farm on which ostriches are bred for the
      sake of their feathers, oil, eggs, etc.

   Ostrich farming, the occupation of breeding ostriches for
      the sake of their feathers, etc.

   Ostrich fern (Bot.) a kind of fern (Onoclea
      Struthiopteris), the tall fronds of which grow in a
      circle from the rootstock. It is found in alluvial soil in
      Europe and North America.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ostrich
    n 1: a person who refuses to face reality or recognize the truth
         (a reference to the popular notion that the ostrich hides
         from danger by burying its head in the sand)
    2: fast-running African flightless bird with two-toed feet;
       largest living bird [syn: ostrich, Struthio camelus]

The Devil's Dictionary (1881-1906):

OSTRICH, n.  A large bird to which (for its sins, doubtless) nature
has denied that hinder toe in which so many pious naturalists have
seen a conspicuous evidence of design.  The absence of a good working
pair of wings is no defect, for, as has been ingeniously pointed out,
the ostrich does not fly.