irritant vs pain

irritant and pain both are nouns.

Word	Noun	Adjective	Verb	Adverb
irritant	Yes	No	No	No
pain	Yes	No	Yes	No

As nouns, pain is a hypernym of irritant; that is, pain is a word with a broader meaning than irritant:

Other hypernyms of irritant include annoyance, bother, botheration, infliction, nuisance, pain in the ass, pain in the neck.

irritant (noun)	pain (noun)
something that causes irritation and annoyance	a somatic sensation of acute discomfort
	something or someone that causes trouble; a source of unhappiness
	emotional distress; a fundamental feeling that people try to avoid
	a symptom of some physical hurt or disorder

irritant (verb)	pain (verb)
	cause bodily suffering to and make sick or indisposed
	cause emotional anguish or make miserable