The Collaborative International Dictionary of English v.0.48:

aepyornis \aepyornis\, AEpyornis \[AE]`py*or"nis\, n. [Gr. ?
   high + ? bird.]
   A gigantic (to 9 ft.) extinct flightless bird, of which
   fossils were found in Madagascar.

   Syn: elephant bird
        [1913 Webster + WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Epiornis \Ep`i*or"nis\, n. [NL.: cf. F. ['e]piornis. See
   [AE]pyornis.] (Zo["o]l.)
   One of the gigantic ostrichlike birds of the genus
   [AE]piornis, only recently extinct. Its remains have been
   found in Madagascar. [Written also [AE]pyornis.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

aepyornis
    n 1: huge (to 9 ft.) extinct flightless bird of Madagascar [syn:
         elephant bird, aepyornis]