The Collaborative International Dictionary of English v.0.48:

Dialect \Di"a*lect\, n. [F. dialecte, L. dialectus, fr. Gr. ?,
   fr. ? to converse, discourse. See Dialogue.]
   1. Means or mode of expressing thoughts; language; tongue;
      form of speech.
      [1913 Webster]

            This book is writ in such a dialect
            As may the minds of listless men affect.
            Bunyan.
            The universal dialect of the world.   --South.
      [1913 Webster]

   2. The form of speech of a limited region or people, as
      distinguished from ether forms nearly related to it; a
      variety or subdivision of a language; speech characterized
      by local peculiarities or specific circumstances; as, the
      Ionic and Attic were dialects of Greece; the Yorkshire
      dialect; the dialect of the learned.
      [1913 Webster]

            In the midst of this Babel of dialects there
            suddenly appeared a standard English language.
                                                  --Earle.
      [1913 Webster]

            [Charles V.] could address his subjects from every
            quarter in their native dialect.      --Prescott.

   Syn: Language; idiom; tongue; speech; phraseology. See
        Language, and Idiom.
        [1913 Webster]

WordNet (r) 3.0 (2006):

dialect
    n 1: the usage or vocabulary that is characteristic of a
         specific group of people; "the immigrants spoke an odd
         dialect of English"; "he has a strong German accent"; "it
         has been said that a language is a dialect with an army and
         navy" [syn: dialect, idiom, accent]