The Collaborative International Dictionary of English v.0.48:

Mortally \Mor"tal*ly\, adv.
   1. In a mortal manner; so as to cause death; as, mortally
      wounded.
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   2. In the manner of a mortal or of mortal beings.
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            I was mortally brought forth.         --Shak.
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   3. In an extreme degree; to the point of dying or causing
      death; desperately; as, mortally jealous.
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            Adrian mortally envied poets, painters, and
            artificers, in works wherein he had a vein to excel.
                                                  --Bacon.
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WordNet (r) 3.0 (2006):

mortally
    adv 1: 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"