Source : Webster's Revised Unabridged Dictionary (1913)

Mortally \Mor"tal*ly\, adv.
   1. In a mortal manner; so as to cause death; as, mortally
      wounded.

   2. In the manner of a mortal or of mortal beings.

            I was mortally brought forth.         --Shak.

   3. In an extreme degree; to the point of dying or causing
      death; desperately; as, mortally jealous.

            Adrian mortally envied poets, painters, and
            artificers, in works wherein he had a vein to excel.
                                                  --Bacon.

Source : WordNet®

mortally
     adv : in such a manner that death ensues (also in reference to
           hatred, jealousy, fear, etc.); "a being of whom the
           forest Indians are said to be mortally afraid, with a
           hoof shaped like the heel of a bottle"