The Collaborative International Dictionary of English v.0.48:

Auk \Auk\, n. [Prov. E. alk; akin to Dan. alke, Icel. & Sw.
   alka.] (Zool.)
   A name given to various species of arctic sea birds of the
   family Alcid[ae]. The great auk, now extinct, is Alca
   impennis (or Plautus impennis) . The razor-billed auk is
   Alca torda. See Puffin, Guillemot, and Murre.
   [1913 Webster]

WordNet (r) 3.0 (2006):

auk
    n 1: black-and-white short-necked web-footed diving bird of
         northern seas