The Collaborative International Dictionary of English v.0.48:

Greek \Greek\, a. [AS. grec, L. Graecus, Gr. ?: cf. F. grec. Cf.
   Grecian.]
   Of or pertaining to Greece or the Greeks; Grecian.
   [1913 Webster]

   Greek calends. See under Greek calends in the vocabulary.


   Greek Church (Eccl. Hist.), the Eastern Church; that part
      of Christendom which separated from the Roman or Western
      Church in the ninth century. It comprises the great bulk
      of the Christian population of Russia (of which this is
      the established church), Greece, Moldavia, and Wallachia.
      The Greek Church is governed by patriarchs and is called
      also the Byzantine Church.

   Greek cross. See Illust. (10) Of Cross.

   Greek Empire. See Byzantine Empire.

   Greek fire, a combustible composition which burns under
      water, the constituents of which are supposed to be
      asphalt, with niter and sulphur. --Ure.

   Greek rose, the flower campion.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Greek cross
    n 1: a cross with each of the four arms the same length