Source : Webster's Revised Unabridged Dictionary (1913)

Mystic \Mys"tic\, Mystical \Mys"tic*al\, a. [L. mysticus, Gr. ?
   belonging to secret rites, from ? one initiated: cf. F.
   mystique. See 1st {Mystery}, {Misty}.]
   1. Remote from or beyond human comprehension; baffling human
      understanding; unknowable; obscure; mysterious.

            Heaven's numerous hierarchy span The mystic gulf
            from God to man.                      --Emerson.

            God hath revealed a way mystical and supernatural.
                                                  --Hooker.

   2. Importing or implying mysticism; involving some secret
      meaning; allegorical; emblematical; as, a mystic dance;
      mystic Babylon.

            Thus, then, did the spirit of unity and meekness
            inspire every joint and sinew of the mystical body.
                                                  --Milton.
      -- {Mys"tic*al*ly}, adv. -- {Mys"tic*al*ness}, n.

Source : WordNet®

mystically
     adv : in a mystical manner; "chant mystically"