The Collaborative International Dictionary
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.]
Subject to death; destined to die; as, man is mortal.
Destructive to life; causing or occasioning death; terminating life; exposing to or deserving death; deadly; as, a mortal wound; a mortal sin.
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Fatally vulnerable; vital.
Last of all, against himself he turns his sword, but missing the mortal place, with his poniard finishes the work.
--Milton. -
Of or pertaining to the time of death.
Safe in the hand of one disposing Power, Or in the natal or the mortal hour.
--Pope. -
Affecting as if with power to kill; deathly.
The nymph grew pale, and in a mortal fright.
--Dryden. -
Human; belonging to man, who is mortal; as, mortal wit or knowledge; mortal power.
The voice of God To mortal ear is dreadful.
--Milton. -
Very painful or tedious; wearisome; as, a sermon lasting two mortal hours. [Colloq.]
--Sir W. Scott.Mortal foe, Mortal enemy, an inveterate, desperate, or implacable enemy; a foe bent on one's destruction.
WordNet
n. an enemy who wants to kill you
Usage examples of "mortal enemy".
If we strike him down now, while his alliances are weak and disordered, we risk giving all of Navahk to Bahnak of Hurgrum, and Bahnak will be our mortal enemy so long as he draws breath.
They scarcely even thought about the lost southern lands, for they had never lived there, and thus of all the Twilight People they had suffered the least at the hands of the mortal enemy.
If the abortion had worked, she and Templeton wouldn't have been there and she'd be Nancy's mortal enemy.
But I had then, that night, in that room, one mortal enemy, one enemy sworn and implacable and already bloody-handed.
Taita knew him well: to him Apepi was the invader, the bloody barbarian, mortal enemy of his country and his Pharaoh.