Gesundheit is an interjection used to wish good health to someone who has just sneezed. It comes from German, where it means, literally, health, and in German it is used as the equivalent of the English God bless you or bless you. It came to English around the start of the 20th century via German and Jewish communities in the United States.1 It was common in the U.S. by the 1920s and has stayed fairly common there,2 but it remains rare elsewhere in the English-speaking world.
My street in this small former mill town is crowded enough that when someone sneezes in a backyard, the person next door is likely to say “gesundheit.” [New York Times]
What is the atheist equivalent of “bless you” when someone sneezes? Gesundheit! [Guardian]
Near the tip of the Cape, there’s an old joke about it: sneeze on the west side and they’ll say gesundheit on the east. [Boston Globe]
Woe to the polite candidate who blesses his sneezing competitor with a Gesundheit or wishes bon appétit when breaking bread. [letter to Economist]
1. Gesundheit in the OED ↩
2. Google Ngram graphing “Gesundheit” in American books and journals, 1800-2000 ↩