harmful vs ill

harmful is not a noun while ill is a noun.

Word	Noun	Adjective	Verb	Adverb
harmful	No	Yes	No	No
ill	Yes	Yes	No	Yes

harmful (noun)	ill (noun)
	an often persistent bodily disorder or disease; a cause for complaining

harmful (adjective)	ill (adjective)
causing or capable of causing harm	affected by an impairment of normal physical or mental function
	distressing
	resulting in suffering or adversity
	indicating hostility or enmity
	presaging ill fortune

harmful (adverb)	ill (adverb)
	(`ill' is often used as a combining form) in a poor or improper or unsatisfactory manner; not well
	with difficulty or inconvenience; scarcely or hardly
	unfavorably or with disapproval