The Collaborative International Dictionary of English v.0.48:

Coherence \Co*her"ence\, Coherency \Co*her"en*cy\, n. [L.
   cohaerentia: cf. F. coh['e]rence.]
   1. A sticking or cleaving together; union of parts of the
      same body; cohesion.
      [1913 Webster]

   2. Connection or dependence, proceeding from the
      subordination of the parts of a thing to one principle or
      purpose, as in the parts of a discourse, or of a system of
      philosophy; a logical and orderly and consistent relation
      of parts; consecutiveness.
      [1913 Webster]

            Coherence of discourse, and a direct tendency of all
            the parts of it to the argument in hand, are most
            eminently to be found in him.         --Locke.
      [1913 Webster]

   3. the state of cohering.

   Syn: cohesion, cohesiveness.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

coherence
    n 1: the state of cohering or sticking together [syn:
         coherence, coherency, cohesion, cohesiveness] [ant:
         incoherence, incoherency]
    2: logical and orderly and consistent relation of parts [syn:
       coherence, coherency]

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "coherence":
   accord, accordance, accretion, adherence, adhesion, affinity,
   agglomeration, agglutination, agreement, assent, bond, chorus,
   clarity, clear-cutness, clearness, cling, clinging, clotting,
   clustering, coagulation, cohesion, cohesiveness, coincidence,
   compaction, compatibility, concert, concord, concordance,
   concretion, condensation, conformance, conformation, conformity,
   congealment, congelation, congeniality, conglobation,
   conglomeration, congruence, congruency, congruity, connectedness,
   consistency, consolidation, consonance, consort, cooperation,
   correspondence, crystallinity, definition, directness,
   distinctness, equivalence, explicitness, harmony, impartibility,
   indiscerptibility, indissolubility, indivisibility, infrangibility,
   infusibility, inseparability, insolubility, integrity,
   intersection, junction, limpidity, lucidity, oneness, overlap,
   parallelism, peace, pellucidity, perspicuity, plain English,
   plain speech, plain style, plainness, rapport, self-consistency,
   set, simplicity, solidarity, solidification, sticking,
   straightforwardness, structure, symmetry, sync, synchronism, tally,
   timing, transparency, transpicuity, unadorned style,
   unambiguousness, unequivocalness, uniformity, union, unison,
   unisonance, unity, unmistakableness