The Collaborative International Dictionary of English v.0.48:

Conversation \Con`ver*sa"tion\, n. [OE. conversacio (in senses 1
   & 2), OF. conversacion, F. conversation, fr. L. conversatio
   frequent abode in a place, intercourse, LL. also, manner of
   life.]
   1. General course of conduct; behavior. [Archaic]
      [1913 Webster]

            Let your conversation be as it becometh the gospel.
                                                  --Philip. i.
                                                  27.
      [1913 Webster]

   2. Familiar intercourse; intimate fellowship or association;
      close acquaintance. "Conversation with the best company."
      --Dryden.
      [1913 Webster]

            I set down, out of long experience in business and
            much conversation in books, what I thought pertinent
            to this business.                     --Bacon.
      [1913 Webster]

   3. Commerce; intercourse; traffic. [Obs.]
      [1913 Webster]

            All traffic and mutual conversation.  --Hakluyt.
      [1913 Webster]

   4. Colloquial discourse; oral interchange of sentiments and
      observations; informal dialogue.
      [1913 Webster]

            The influence exercised by his [Johnson's]
            conversation was altogether without a parallel.
                                                  --Macaulay.
      [1913 Webster]

   5. Sexual intercourse; as, criminal conversation.

   Syn: Intercourse; communion; commerce; familiarity;
        discourse; dialogue; colloquy; talk; chat.

   Usage: Conversation, Talk. There is a looser sense of
          these words, in which they are synonymous; there is a
          stricter sense, in which they differ. Talk is usually
          broken, familiar, and versatile. Conversation is more
          continuous and sustained, and turns ordinarily upon
          topics or higher interest. Children talk to their
          parents or to their companions; men converse together
          in mixed assemblies. Dr. Johnson once remarked, of an
          evening spent in society, that there had been a great
          deal of talk, but no conversation.
          [1913 Webster]

WordNet (r) 3.0 (2006):

conversation
    n 1: the use of speech for informal exchange of views or ideas
         or information etc.

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "conversation":
   ESP, accents, answer, chat, chatter, collegiality, colloquy,
   comment, commerce, communication, communion, community,
   confabulation, congress, connection, contact, converse,
   correspondence, dealing, dealings, debate, deliberation, dialogue,
   discourse, discussion, elocution, exchange, fellowship, gab,
   gossip, information, interaction, interchange, intercommunication,
   intercommunion, intercourse, interplay, language,
   linguistic intercourse, message, observation, oral communication,
   palaver, parley, parole, prattle, rapping, remark, repartee, reply,
   response, social activity, social intercourse, social relations,
   speaking, speech, speech circuit, speech situation, talk, talking,
   telepathy, touch, traffic, truck, two-way communication,
   ventilation, words, yakkety-yak, yakking



Easton's 1897 Bible Dictionary:

Conversation
   generally the goings out and in of social intercourse (Eph. 2:3;
   4:22; R.V., "manner of life"); one's deportment or course of
   life. This word is never used in Scripture in the sense of
   verbal communication from one to another (Ps. 50:23; Heb. 13:5).
   In Phil. 1:27 and 3:20, a different Greek word is used. It there
   means one's relations to a community as a citizen, i.e.,
   citizenship.


The Devil's Dictionary (1881-1906):

CONVERSATION, n.  A fair to the display of the minor mental
commodities, each exhibitor being too intent upon the arrangement of
his own wares to observe those of his neighbor.