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]