The Collaborative International Dictionary of English v.0.48:

jocosity \jo*cos"i*ty\ (j[-o]*k[o^]s"[i^]*t[y^]), n.
   A jocose act or saying; jocoseness. --Sir T. Browne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

jocosity
    n 1: fun characterized by humor [syn: jocosity, jocularity]
    2: the trait of merry joking [syn: jocoseness, jocosity,
       merriness, humorousness]