ill vs unwell

ill is a noun but unwell is not a noun.

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

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

ill (adjective)	unwell (adjective)
affected by an impairment of normal physical or mental function	somewhat ill or prone to illness
distressing
resulting in suffering or adversity
indicating hostility or enmity
presaging ill fortune

ill (adverb)	unwell (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