anus vs arse

anus and arse both are nouns.

Word	Noun	Adjective	Verb	Adverb
anus	Yes	No	No	No
arse	Yes	No	No	No

As nouns, arse is a hyponym of anus; that is, arse is a word with a more specific, narrower meaning than anus:

Other hyponyms of anus include arsehole, asshole, bunghole, imperforate anus.

anus (noun)	arse (noun)
the excretory opening at the end of the alimentary canal	vulgar slang for anus
	the fleshy part of the human body that you sit on