Ouroboros

Ouroboros \ôr-rŏb'-ôr-rŭs\ noun: 1. a snake or serpent that forms the shape of a circle by eating its own tail (representing cyclicality, self-reflexivity or the continuous cycle of life and death), 2. a picture or symbol representing this

Etymology: Greek ouroboros tail-eater

Compare this etymology with yesterday’s; they both stem from the ancient Greek word for tail.