Source : Webster's Revised Unabridged Dictionary (1913)

Disadvantageous \Dis*ad`van*ta"geous\, a. [Cf. F.
   d['e]savantageux.]
   Attended with disadvantage; unfavorable to success or
   prosperity; inconvenient; prejudicial; -- opposed to
   {advantageous}; as, the situation of an army is
   disadvantageous for attack or defense.

         Even in the disadvantageous position in which he had
         been placed, he gave clear indications of future
         excellence.                              --Prescott.
   -- {Dis*ad`van*ta"geous*ly}, adv. --
   {Dis*ad`van*ta"geous*ness}, n.

Source : WordNet®

disadvantageously
     adv : in a disadvantageous way; to someone's disadvantage; "the
           venture turned out badly for the investors"; "angry
           that the case was settled disadvantageously for them"
           [syn: {badly}] [ant: {well}, {well}]