The Collaborative International Dictionary of English v.0.48:

Favorable \Fa"vor*a*ble\ (f[=a]"v[~e]r*[.a]*b'l), a. [Written
   also favourable.] [F. favorable, L. favorabilis favored,
   popular, pleasing, fr. favor. See Favor, n.]
   1. Full of favor; favoring; manifesting partiality; kind;
      propitious; friendly.
      [1913 Webster]

            Lend favorable ears to our request.   --Shak.
      [1913 Webster]

            Lord, thou hast been favorable unto thy land. --Ps.
                                                  lxxxv. 1.
      [1913 Webster]

   2. Conducive; contributing; tending to promote or facilitate;
      advantageous; convenient.
      [1913 Webster]

            A place very favorable for the making levies of men.
                                                  --Clarendon.
      [1913 Webster]

            The temper of the climate, favorable to generation,
            health, and long life.                --Sir W.
                                                  Temple.
      [1913 Webster]

   3. Beautiful; well-favored. [Obs.] --Spenser. --
      Fa"vora*ble*ness, n. -- Fa"vor*a*bly, adv.
      [1913 Webster]

            The favorableness of the present times to all
            exertions in the cause of liberty.    --Burke.
      [1913 Webster]

WordNet (r) 3.0 (2006):

favorableness
    n 1: the quality of being encouraging or promising of a
         successful outcome [syn: favorableness, favourableness,
         advantageousness, positivity, positiveness,
         profitableness] [ant: unfavorableness,
         unfavourableness]