I just did a Google Books search on this word for a serpent biting its own tail and the earliest hit I got was 1884, from La Nouvelle revue, Vol. 26:
But of course this is in French, and I was wondering how far back it goes in English. The earliest I see in Google Books is from 1899 (Psychism, by Paul Gibier):
It’s not in my old Compact OED; can anyone with access to the online OED tell me if there’s an entry, and if so what the first cite is?
Edit: I just realized it could also be spelled ouroborus (with the Latin -us ending), and that takes us back to 1897: