The Collaborative International Dictionary of English v.0.48:

Unfavorable \Un*fa"vor*a*ble\, a.
   Not favorable; not propitious; adverse; contrary;
   discouraging. -- Un*fa"vor*a*ble*ness, n. --
   Un*fa"vor*a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unfavorableness
    n 1: the quality of not being encouraging or indicative of
         success [syn: unfavorableness, unfavourableness] [ant:
         advantageousness, favorableness, favourableness,
         positiveness, positivity, profitableness]