ˈā-nəs
Noun
1. An opening at the opposite end of an animal’s digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may include: matter which the animal cannot digest, such as bones; food material after all the nutrients have been extracted, for example cellulose or lignin; ingested matter which would be toxic if it remained in the digestive tract; and dead or excess gut bacteria and other endosymbionts. (wikipedia.org)
2. The posterior opening of the alimentary canal. (merriam-webster.com)
3. (Anatomy)
The lower opening of the alimentary canal, through which feces and flatus are ejected. (wiktionary.org)
Word origin: From Latin anus, meaning “ring, anus”, which is from the Proto-Indo-European ano–, meaning “ring”