The Collaborative International Dictionary of English v.0.48:

Correspondence \Cor`re*spond"ence\ (-sp?nd"ens), n. [Cf. F.
   correspondance.]
   1. Friendly intercourse; reciprocal exchange of civilities;
      especially, intercourse between persons by means of
      letters.
      [1913 Webster]

            Holding also good correspondence with the other
            great men in the state.               --Bacon.
      [1913 Webster]

            To facilitate correspondence between one part of
            London and another, was not originally one of the
            objects of the post office.           --Macaulay.
      [1913 Webster]

   2. The letters which pass between correspondents.
      [1913 Webster]

   3. Mutual adaptation, relation, or agreement, of one thing to
      another; agreement; congruity; fitness; relation.
      [1913 Webster]

WordNet (r) 3.0 (2006):

correspondence
    n 1: communication by the exchange of letters
    2: compatibility of observations; "there was no agreement
       between theory and measurement"; "the results of two tests
       were in correspondence" [syn: agreement, correspondence]
    3: the relation of corresponding in degree or size or amount
       [syn: commensurateness, correspondence,
       proportionateness]
    4: (mathematics) an attribute of a shape or relation; exact
       reflection of form on opposite sides of a dividing line or
       plane [syn: symmetry, symmetricalness, correspondence,
       balance] [ant: asymmetry, dissymmetry, imbalance]
    5: similarity by virtue of corresponding [syn: parallelism,
       correspondence]

Moby Thesaurus II by Grady Ward, 1.0:

293 Moby Thesaurus words for "correspondence":
   ESP, PP, RD, RFD, accommodation, accompaniment, accord, accordance,
   account, acquiescence, adaptation, adaption, adjustment, affinity,
   agape, agreement, airmail, alikeness, alliance, amity, analogy,
   annals, answer, aping, approach, approximation, assent,
   assimilation, association, balance, bilateral symmetry,
   bonds of harmony, book post, brotherly love, cahoots, calm,
   caritas, catalog, cement of friendship, charity, chorus, chronicle,
   closeness, co-working, coaction, coequality, coextension,
   coherence, coincidence, collaboration, collectivity, collusion,
   combination, combined effort, commerce, communication, communion,
   community, community of interests, comparability, comparison,
   compatibility, compliance, concert, concerted action, concomitance,
   concord, concordance, concourse, concurrence, confluence,
   conformance, conformation, conformation other-direction,
   conformity, congeniality, congress, congruence, congruency,
   congruity, conjunction, connection, consilience, consistency,
   consonance, consort, conspiracy, constancy, contact, continuity,
   conventionality, conversation, converse, cooperation, copying,
   corelation, correlation, correlativism, correlativity, dealing,
   dealings, direct mail, direct-mail selling, documentation,
   dynamic symmetry, empathy, equability, equality, equanimity,
   equation, equilibrium, equipoise, equipollence, equiponderance,
   equity, equivalence, equivalency, esprit, esprit de corps,
   eurythmics, eurythmy, evenness, exchange, express,
   feeling of identity, fellow feeling, fellowship, finish,
   flexibility, fourth-class mail, frank, frictionlessness,
   good vibes, good vibrations, halfpenny post, happy family, harmony,
   history, homogeneity, homoousia, identity, imitation,
   indistinguishability, information, interaction, interchange,
   intercommunication, intercommunion, intercourse, interplay,
   intersection, inventory, inverse proportion, inverse ratio,
   inverse relationship, junction, junk mail, justice, keeping,
   kinship, letter post, letters, levelness, like-mindedness,
   likeness, likening, line, linguistic intercourse, list, love, mail,
   mail-order selling, mailing list, malleability, memorial, message,
   mimicking, monolithism, multilateral symmetry, mutuality, nearness,
   newspaper post, no difference, obedience, observance, oneness,
   orthodoxy, overlap, par, parallelism, parasitism, parcel post,
   parity, peace, persistence, pipe roll, pliancy, poise, polarity,
   post, post day, proportion, proportionality, rapport,
   rapprochement, reciprocality, reciprocation, reciprocity,
   reconcilement, reconciliation, record, recording, register,
   registered mail, registry, regularity, relativity, relic, remains,
   reply, resemblance, response, roll, rolls, roster, rota,
   rural delivery, rural free delivery, sameness, saprophytism,
   scroll, sea mail, seapost, self-consistency, self-identity,
   selfhood, selfness, selfsameness, semblance, shapeliness, sharing,
   similarity, simile, similitude, simulation, simultaneity,
   social intercourse, solidarity, speaking, special delivery,
   special handling, speech, speech circuit, speech situation,
   stability, steadfastness, steadiness, strictness, surface mail,
   symbiosis, symmetricalness, symmetry, sympathy, symphony, sync,
   synchronism, synergy, synonymity, synonymousness, synonymy, table,
   talking, tally, team spirit, telepathy, timing, token, touch,
   trace, traditionalism, traffic, trilateral symmetry, truck,
   two-way communication, understanding, uniformity, union, unison,
   unisonance, united action, unity, unruffledness, vestige



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CORRESPONDENCE. The letters written by one to another, and the answers
thereto, make what is called the correspondence of the parties.
     2. In general, the correspondence of the parties contains the best
evidence of the facts to which it relates. See Letter, contracts; Proposal.
     3. When an offer to contract is made by letter, it must be accepted
unconditionally for if the precise terms are changed, even in the slightest
degree, there is no contract. 1 Bouv. Inst. n. 904. See, as to the power of
revoking an offer made by letter, 1 Bouv. Inst. n. 933.