mortalis

Mortalis, mortale is a third declension adjective of two terminations: masculine and feminine share mortalis, only the neuter differs. It is an i-stem, so the ablative singular is mortali, the genitive plural mortalium and the neuter plural mortalia.

Used as a noun in the plural it simply means human beings, and genitives like mortalium are a common poetic substitute for hominum where the metre will not take it. Its opposite immortalis is the standing epithet of the gods, and di immortales is the Roman equivalent of "good heavens" - an exclamation, not a theological claim. English mortal came through French with the sense untouched.