pain vs irritant

pain and irritant both are nouns.

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

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

Other hyponyms of pain include nuisance, thorn, plague.

pain (noun)	irritant (noun)
a somatic sensation of acute discomfort	something that causes irritation and annoyance
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

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