pain in the ass vs annoyance

pain in the ass and annoyance both are nouns.

Word	Noun	Adjective	Verb	Adverb
pain in the ass	Yes	No	No	No
annoyance	Yes	No	No	No

As nouns, pain in the ass and annoyance are synonyms defined as:

pain in the ass and annoyance: something or someone that causes trouble; a source of unhappiness

Other synonyms of pain in the ass include bother, botheration, infliction, nuisance, pain, pain in the neck.

pain in the ass (noun)	annoyance (noun)
something or someone that causes trouble; a source of unhappiness	the act of troubling or annoying someone
	something or someone that causes trouble; a source of unhappiness
	anger produced by some annoying irritation
	an unpleasant person who is annoying or exasperating
	the psychological state of being irritated or annoyed