aching vs painful

aching is a noun but painful is not a noun.

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

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

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