What does "disadvantageous" mean?

Disadvantageous: 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.