pestilential (adj.)

c. 1300, "any infectious or contagious disease, fatal epidemic," from Old French pestilence "plague, epidemic" (12c.) and directly from Latin pestilentia "a plague, an unwholesome atmosphere," noun of condition from pestilentem (nominative pestilens) "infected, unwholesome, noxious," from pestis "deadly disease, plague" (see pest).

Also in Middle English "wickedness, evil, sin, a vice, that which is morally pestilential."