Source : Webster's Revised Unabridged Dictionary (1913)

Obstacle \Ob"sta*cle\, n. [F., fr. L. obstaculum, fr. obstare to
   withstand, oppose; ob (see {Ob-}) + stare to stand. See
   {Stand}. and cf. {Oust}, v.]
   That which stands in the way, or opposes; anything that
   hinders progress; a hindrance; an obstruction, physical or
   moral.

         If all obstacles were cut away. And that my path were
         even to the crown.                       --Shak.

   Syn: Impediment; obstuction; hindrance; difficulty. See
        {Impediment}, and {Obstruction}.

Source : WordNet®

obstacle
     n 1: something immaterial that stands in the way and must be
          circumvented or surmounted; "lack of immagination is an
          obstacle to one's advancement"; "the poverty of a
          district is an obstacle to good education"; "the
          filibuster was a major obstruction to the success of
          their plan" [syn: {obstruction}]
     2: an obstruction that stands in the way (and must be removed
        or surmounted or circumvented)