The Collaborative International Dictionary of English v.0.48:

Comity \Com"i*ty\, n.; pl. Comities. [L. comitas, fr. comis
   courteous, kind.]
   Mildness and suavity of manners; courtesy between equals;
   friendly civility; as, comity of manners; the comity of
   States.
   [1913 Webster]

   Comity of nations (International Law), the courtesy by
      which nations recognize within their own territory, or in
      their courts, the peculiar institutions of another nation
      or the rights and privileges acquired by its citizens in
      their own land. By some authorities private international
      law rests on this comity, but the better opinion is that
      it is part of the common law of the land, and hence is
      obligatory as law.

   Syn: Civility; good breeding; courtesy; good will.
        [1913 Webster]

WordNet (r) 3.0 (2006):

comity of nations
    n 1: courteous respect by one nation for the laws and
         institutions of another