mortal : Idioms & Phrases
mortal enemy
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noun an enemy who wants to kill you
WordNet
Mortal foe , Mortal enemy
- an inveterate, desperate, or implacable enemy; a foe bent on one's destruction.
Webster 1913
mortal sin
-
noun an unpardonable sin entailing a total loss of grace
deadly sin.
- theologians list seven mortal sins