The Collaborative International Dictionary of English v.0.48:

Mortal \Mor"tal\, n.
   A being subject to death; a human being; man. "Warn poor
   mortals left behind." --Tickell.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mortal \Mor"tal\, a. [F. mortel, L. mortalis, from mors, mortis,
   death, fr. moriri 8die; akin to E. murder. See Murder, and
   cf. Filemot, Mere a lake, Mortgage.]
   1. Subject to death; destined to die; as, man is mortal.
      [1913 Webster]

   2. Destructive to life; causing or occasioning death;
      terminating life; exposing to or deserving death; deadly;
      as, a mortal wound; a mortal sin.
      [1913 Webster]

   3. Fatally vulnerable; vital.
      [1913 Webster]

            Last of all, against himself he turns his sword, but
            missing the mortal place, with his poniard finishes
            the work.                             --Milton.
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   4. Of or pertaining to the time of death.
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            Safe in the hand of one disposing Power,
            Or in the natal or the mortal hour.   --Pope.
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   5. Affecting as if with power to kill; deathly.
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            The nymph grew pale, and in a mortal fright.
                                                  --Dryden.
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   6. Human; belonging to man, who is mortal; as, mortal wit or
      knowledge; mortal power.
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            The voice of God
            To mortal ear is dreadful.            --Milton.
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   7. Very painful or tedious; wearisome; as, a sermon lasting
      two mortal hours. [Colloq.] --Sir W. Scott.
      [1913 Webster]

   Mortal foe, Mortal enemy, an inveterate, desperate, or
      implacable enemy; a foe bent on one's destruction.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mortal
    adj 1: subject to death; "mortal beings" [ant: immortal]
    2: involving loss of divine grace or spiritual death; "the seven
       deadly sins" [syn: deadly, mortal(a)]
    3: unrelenting and deadly; "mortal enemy"
    4: causing or capable of causing death; "a fatal accident"; "a
       deadly enemy"; "mortal combat"; "a mortal illness" [syn:
       deadly, deathly, mortal]
    n 1: a human being; "there was too much for one person to do"
         [syn: person, individual, someone, somebody,
         mortal, soul]

Moby Thesaurus II by Grady Ward, 1.0:

149 Moby Thesaurus words for "mortal":
   Adamite, Adamitic, abject, anthropocentric, anthropological, awful,
   baneful, being, bitter, bodily, body, brittle, brutal, capricious,
   cat, changeable, chap, character, conceivable, corporal, corporeal,
   corruptible, cracking, creature, customer, deadly, death-bringing,
   deathful, deathly, deciduous, destructive, dire, disastrous, duck,
   dying, earthling, earthly, earthy, enormous, ephemeral, evanescent,
   extreme, fading, fantastic, fatal, fellow, feral, fickle, finite,
   fleeting, fleshly, flitting, fly-by-night, flying, fragile, frail,
   fugacious, fugitive, great, groundling, guy, hand, head, hominal,
   homo, homocentric, human, human being, humanistic, impermanent,
   impetuous, implacable, impulsive, inconstant, individual,
   inordinate, insubstantial, intense, internecine, joker, killing,
   lethal, life, likely, living soul, malign, malignant, man,
   man-centered, massive, merciless, momentary, monumental, mutable,
   nondurable, nonpermanent, nose, one, only human, party, passing,
   perishable, pernicious, person, personage, personality, pestilent,
   pestilential, physical, possible, prodigious, relentless, ruthless,
   savage, short-lived, single, somebody, someone, soul, stupendous,
   subject to death, sworn, tellurian, temporal, temporary, terminal,
   terran, terrible, towering, transient, transitive, transitory,
   tremendous, unangelic, unappeasable, unceasing, undurable,
   unenduring, unflinching, unrelenting, unremitting, unstable,
   unyielding, virulent, volatile, weak, woman, worldling, worldly