The Collaborative International Dictionary of English v.0.48:

Congruity \Con*gru"i*ty\ (? or ?), n.; pl. Congruities. [Cf.
   F. congruit?.]
   1. The state or quality of being congruous; the relation or
      agreement between things; fitness; harmony;
      correspondence; consistency.
      [1913 Webster]

            With what congruity doth the church of Rome deny
            that her enemies do at all appertain to the church
            of Christ?                            --Hooker.
      [1913 Webster]

            A whole sentence may fail of its congruity by
            wanting one particle.                 --Sir P.
                                                  Sidney.
      [1913 Webster]

   2. (Geom.) Coincidence, as that of lines or figures laid over
      one another.
      [1913 Webster]

   3. (Scholastic Theol.) That, in an imperfectly good persons,
      which renders it suitable for God to bestow on him gifts
      of grace.
      [1913 Webster]

WordNet (r) 3.0 (2006):

congruity
    n 1: the quality of agreeing; being suitable and appropriate
         [syn: congruity, congruousness, congruence] [ant:
         incongruity, incongruousness]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "congruity":
   accommodation, accord, accordance, acquiescence, adaptation,
   adaption, adjustment, affinity, agreement, assent, balance,
   bilateral symmetry, chorus, coherence, coincidence, compatibility,
   compliance, concert, concord, concordance, conformance,
   conformation, conformation other-direction, conformity,
   congeniality, congruence, congruency, consistency, consonance,
   consort, conventionality, cooperation, correspondence,
   dynamic symmetry, equality, equilibrium, equivalence, eurythmics,
   eurythmy, evenness, finish, flexibility, harmony, intersection,
   keeping, line, malleability, multilateral symmetry, obedience,
   observance, oneness, orthodoxy, overlap, parallelism, peace,
   pliancy, polarity, proportion, proportionality, rapport,
   reconcilement, reconciliation, regularity, self-consistency,
   shapeliness, strictness, symmetricalness, symmetry, sync,
   synchronism, tally, timing, traditionalism, trilateral symmetry,
   uniformity, union, unison, unisonance