The Collaborative International Dictionary of English v.0.48:

Apteryx \Ap"te*ryx\, n. [Gr. 'a priv. + pte`ryx wing. Cf.
   Aptera.] (Zool.)
   A genus of New Zealand birds about the size of a hen, with
   only short rudiments of wings, armed with a claw and without
   a tail; the kiwi. It is allied to the gigantic extinct moas
   of the same country. Five species are known.
   [1913 Webster]

WordNet (r) 3.0 (2006):

apteryx
    n 1: nocturnal flightless bird of New Zealand having a long neck
         and stout legs; only surviving representative of the order
         Apterygiformes [syn: kiwi, apteryx]