'annulus' originates from Latin, specifically the word 'annulus', where the root 'ann-' referred to a ring or small ring.

'annulus' passed into English from Medieval/Scientific Latin as 'annulus'; the modern English form 'annulus' (and the Latin plural 'annuli') has been used in technical contexts since the Renaissance.

Initially it meant 'small ring' in Latin, but over time it has come to denote ring-shaped structures or regions in anatomy, mathematics, and biology.