1914, from Ger., lit. "health!" Also in toast auf ihre Gesundheit "to your health" (see sound (adj.)). Lith. aciu, echoic of the sound of a sneeze, has come to mean "good luck, God bless you." See also God.
George, the topic of what one says when someone sneezes has been discussed many times on the site. In future, please search the site first with a keyword or two before posting a discusssion on a topic that has already been discussed many times before.
I'm only a minor deity here, so my wrath only extends within the confines of the site. The only worship I ask is the occasional tossing of some good chocolate in my direction. Even then, that's not required, and doesn't give anyone Chosen status.
I can't think of one of the earlier sneeze discussions that has been closed (for example, and not to flagellate George), so it would be easy to revive them. Here the convention is to revive an old discussion, unless your proposed topic takes a new and different spin on an old issue.
Etymology: German, literally, health, from gesund healthy
It's what I grew up saying and what I began saying even more often after taking a German class and learning it's actual definition. Also, it doesn't bother me that it has come to mean God Bless you, I like to chalk that up to people's ignorance and hearing people tell me it means that just makes me giggle.