The Collaborative International Dictionary of English v.0.48:

Amiability \A`mi*a*bil"i*ty\, n.
   The quality of being amiable; amiableness; sweetness of
   disposition.
   [1913 Webster]

         Every excellency is a degree of amiability. --Jer.
                                                  Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

amiability
    n 1: a cheerful and agreeable mood [syn: good humor, good
         humour, good temper, amiability] [ant: distemper,
         ill humor, ill humour]
    2: a disposition to be friendly and approachable (easy to talk
       to) [syn: affability, affableness, amiability,
       amiableness, bonhomie, geniality]