The Collaborative International Dictionary of English v.0.48:

ivorybill \i"vo*ry*bill`\, Ivory-bill
\I"vo*ry-bill`\([imac]"v[-o]*r[y^]*b[i^]l`), n. (Zool.)
   A large, handsome, black-and-white North American woodpecker
   (Campephilus principalis), having a large, sharp,
   ivory-colored beak. Its general color is glossy black, with
   white secondaries, and a white dorsal stripe. The male has a
   large, scarlet crest. It is now rare, and found only in the
   Gulf States and Cuba.

   Syn: ivory-billed woodpecker, Campephilus principalis.
        [1913 Webster]

WordNet (r) 3.0 (2006):

ivorybill
    n 1: large black-and-white woodpecker of southern United States
         and Cuba having an ivory bill; nearly extinct [syn:
         ivorybill, ivory-billed woodpecker, Campephilus
         principalis]