The Collaborative International Dictionary of English v.0.48:

Congeniality \Con*ge`ni*al"i*ty\ (? or ?; 106), n.
   The state or quality of being congenial; natural affinity;
   adaptation; suitableness. --Sir J. Reynolds.
   [1913 Webster]

         If congeniality of tastes could have made a marriage
         happy, that union should have been thrice blessed.
                                                  --Motley.
   [1913 Webster]

   2. Compatibility between persons.

   Syn: congenialness.
        [WordNet 1.5]

   3. The personality trait of being friendly to a conspicuous
      degree.

   Syn: geniality.
        [PJC]

   4. The personality trait of being likable or pleasant.

   Syn: pleasantness, likability.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

congeniality
    n 1: compatibility between persons [syn: congenialness,
         congeniality]
    2: a congenial disposition [ant: uncongeniality]

Moby Thesaurus II by Grady Ward, 1.0:

140 Moby Thesaurus words for "congeniality":
   accord, accordance, affability, affinity, agape, agreeability,
   agreeableness, agreement, amenity, amiability, amiableness,
   amicability, amicableness, amity, assent, bliss, blissfulness,
   bonds of harmony, brotherly love, caritas, cement of friendship,
   charity, chorus, civility, clubbability, clubbishness, clubbism,
   coherence, coincidence, communicativeness, communion, community,
   community of interests, companionability, compatibility,
   complaisance, concert, concord, concordance, conformance,
   conformation, conformity, congeneracy, congruence, congruency,
   congruity, connateness, connaturality, connaturalness, connature,
   consistency, consonance, consort, cooperation, cordiality,
   correspondence, courtesy, empathy, enjoyableness, equivalence,
   esprit, esprit de corps, familiarity, family favor,
   family likeness, feeling of identity, felicitousness,
   fellow feeling, fellowship, fondness for society, frictionlessness,
   friendliness, friendship, generic resemblance, geniality,
   good vibes, good vibrations, goodliness, goodness, graciousness,
   gregariousness, happy family, harmoniousness, harmony, hospitality,
   identity, intersection, intimacy, kindness, kinship,
   like-mindedness, love, mellifluousness, mellowness, mutuality,
   neighborlikeness, neighborliness, niceness, oneness, overlap,
   parallelism, peace, peaceableness, pleasance, pleasantness,
   pleasantry, pleasingness, pleasurability, pleasurableness,
   pleasure, pleasurefulness, rapport, rapprochement, reciprocity,
   self-consistency, sharing, sociability, sociableness, social grace,
   sociality, solidarity, sweetness, symmetry, sympathy, symphony,
   sync, synchronism, tally, team spirit, timing, understanding,
   unhostility, uniformity, union, unison, unisonance, unity,
   urbanity, welcomeness, well-affectedness