Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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; consecutiveness.

            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.

Source : WordNet®

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