Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

unfavorable
     adj 1: not encouraging or approving or pleasing; "unfavorable
            conditions"; "an unfavorable comparison"; "unfavorable
            comments" [syn: {unfavourable}] [ant: {favorable}]
     2: (of winds or weather) tending to hinder or oppose;
        "unfavorable winds" [syn: {unfavourable}] [ant: {favorable}]
     3: not favorable; "made an unfavorable impression";
        "unfavorable reviews"