painful vs aching

painful is not a noun while aching is a noun.

Word	Noun	Adjective	Verb	Adverb
painful	No	Yes	No	No
aching	Yes	Yes	No	No

painful (noun)	aching (noun)
	a dull persistent (usually moderately intense) pain

painful (adjective)	aching (adjective)
causing physical or psychological pain	causing a dull and steady pain
exceptionally bad or displeasing
causing physical discomfort
causing misery or pain or distress