Source : Webster's Revised Unabridged Dictionary (1913)

Gordian \Gor"di*an\, a.
   1. Pertaining to Gordius, king of Phrygia, or to a knot tied
      by him; hence, intricate; complicated; inextricable.

   {Gordian knot}, an intricate knot tied by Gordius in the
      thong which connected the pole of the chariot with the
      yoke. An oracle having declared that he who should untie
      it should be master of Asia, Alexander the Great averted
      the ill omen of his inability to loosen it by cutting it
      with his sword. Hence, a Gordian knot is an inextricable
      difficulty; and to cut the Gordian knot is to remove a
      difficulty by bold and energetic measures.

   2. (Zo["o]l.) Pertaining to the Gordiacea.

Source : WordNet®

Gordian knot
     n 1: any very difficult problem; insoluble in its own terms
     2: an intricate knot tied by Gordius, the king of Phrygia, and
        cut by the sword of Alexander the Great after he heard
        that whoever undid it would become ruler of Asia