The Collaborative International Dictionary of English v.0.48:

obesity \o*bes"i*ty\, n.[L. obesitas: cf. F. ob['e]sit['e].]
   The state or quality of being obese; excessive body weight;
   incumbrance of flesh.
   [1913 Webster]

WordNet (r) 3.0 (2006):

obesity
    n 1: more than average fatness [syn: fleshiness, obesity,
         corpulency]