anus vs bunghole

anus and bunghole both are nouns.

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

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

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

anus (noun)	bunghole (noun)
the excretory opening at the end of the alimentary canal	a hole in a barrel or cask; used to fill or empty it
	vulgar slang for anus