1914, from German Gesundheit, literally "health!", from Old High German gisunt, gisunti "healthy" (see sound (adj.)). Also in the German toast auf ihre Gesundheit "to your health." Lithuanian aciu, echoic of the sound of a sneeze, has come to mean "good luck, God bless you." God bless you after someone sneezes is credited to St. Gregory the Great, but the pagan Romans (Absit omen) and Greeks had similar customs.
