The Collaborative International Dictionary of English v.0.48:

Ibis \I"bis\, n. [L. ibis, Gr. ?; of Egyptian origin.] (Zool.)
   Any bird of the genus Ibis and several allied genera, of
   the family Ibid[ae], inhabiting both the Old World and the
   New. Numerous species are known. They are large, wading
   birds, having a long, curved beak, and feed largely on
   reptiles.
   [1913 Webster]

   Note: The sacred ibis of the ancient Egyptians (Ibis
         aethiopica) has the head and neck black, without
         feathers. The plumage of the body and wings is white,
         except the tertiaries, which are lengthened and form a
         dark purple plume. In ancient times this bird was
         extensively domesticated in Egypt, but it is now seldom
         seen so far north. The glossy ibis (Plegadis
         autumnalis), which is widely distributed both in the
         Old World and the New, has the head and neck feathered,
         except between the eyes and bill; the scarlet ibis
         (Guara rubra) and the white ibis (Guara alba)
         inhabit the West Indies and South America, and are
         rarely found in the United States. The wood ibis
         (Tantalus loculator) of America belongs to the Stork
         family (Ciconid[ae]). See Wood ibis.
         [1913 Webster]

WordNet (r) 3.0 (2006):

ibis
    n 1: wading birds of warm regions having long slender down-
         curved bills