pain vs ail

pain and ail both are nouns.

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

As verbs, pain and ail are synonyms defined as:

Other synonyms of pain include trouble.

pain (noun)	ail (noun)
a somatic sensation of acute discomfort	aromatic bulb used as seasoning
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)	ail (verb)
cause bodily suffering to and make sick or indisposed	be ill or unwell
cause emotional anguish or make miserable	cause bodily suffering to and make sick or indisposed