Why is the ninth month called September?
c.1300, 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).
pestilence pes·ti·lence (pěs'tə-ləns)
A usually fatal epidemic disease, especially bubonic plague.
An epidemic of such a disease.