plague

Where it comes from

Plague ordinarily means a serious infectious disease, or anything causing widespread and persistent harm. Plague entered Middle English through Late Latin plaga, pestilence, from Latin plaga, a blow or stroke, related to plangere, to strike. The earliest English word could denote a blow, slaughter, calamity, or devastating epidemic. Because the core image was an affliction that struck, plague was never limited neatly to one infection. It could name biblical scourges, epidemics generally, a destructive multitude, or torment.

How the meaning developed

Medicine now also uses plague specifically for disease caused by Yersinia pestis.