'anus' originates from Latin, specifically the word 'ānus', where 'ānus' meant 'ring' or 'circle' and was used for a ring-shaped opening.

'anus' changed from the Latin word 'ānus' (used in Classical and Medieval Latin) and entered English as the modern anatomical term 'anus' via Late Latin/Medieval Latin.

Initially, it meant 'ring' or 'circle' (the sense of a ring-shaped thing), but over time it came to refer specifically to the anatomical opening now called 'anus'.