The Collaborative International Dictionary of English v.0.48:

Dialogue \Di"a*logue\ (?; 115), n. [OE. dialogue, L. dialogus,
   fr. Gr. ?, fr. ? to converse, dia` through + ? to speak: cf.
   F. dialogue. See Legend.]
   1. A conversation between two or more persons; particularly,
      a formal conservation in theatrical performances or in
      scholastic exercises.
      [1913 Webster]

   2. A written composition in which two or more persons are
      represented as conversing or reasoning on some topic; as,
      the Dialogues of Plato.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dialogue \Di"a*logue\, v. i. [Cf. F. dialoguer.]
   To take part in a dialogue; to dialogize. [R.] --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dialogue \Di"a*logue\, v. t.
   To express as in dialogue. [R.]
   [1913 Webster]

         And dialogued for him what he would say. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dialogue
    n 1: a conversation between two persons [syn: dialogue,
         dialog, duologue]
    2: the lines spoken by characters in drama or fiction [syn:
       dialogue, dialog]
    3: a literary composition in the form of a conversation between
       two people; "he has read Plato's Dialogues in the original
       Greek" [syn: dialogue, dialog]
    4: a discussion intended to produce an agreement; "the buyout
       negotiation lasted several days"; "they disagreed but kept an
       open dialogue"; "talks between Israelis and Palestinians"
       [syn: negotiation, dialogue, talks]