The difference between Ill and Unwell

When used as adjectives, ill means evil, whereas unwell means not in good health.

Ill is also noun with the meaning: trouble.

Ill is also adverb with the meaning: not well.

check bellow for the other definitions of Ill and Unwell

Ill as an adjective (obsolete):

Evil; wicked (of people).
Ill as an adjective (archaic):

Morally reprehensible (of behaviour etc.); blameworthy.
Ill as an adjective:

Indicative of unkind or malevolent intentions; harsh, cruel.

Examples:

"He suffered from ill treatment."
Ill as an adjective:

Unpropitious, unkind, faulty, not up to reasonable standard.

Examples:

"'ill manners; ill will"
Ill as an adjective:

Unwell in terms of health or physical condition; sick.

Examples:

"I've been ill with the flu for the past few days."
Ill as an adjective:

Having an urge to vomit.

Examples:

"Seeing those pictures made me ill."
Ill as an adjective (hip-hop slang):

Sublime, with the connotation of being so in a singularly creative way.
Ill as an adjective (slang):

Extremely bad (bad enough to make one ill). Generally used indirectly with to be.

Examples:

"That band was ill."

Ill as a noun (often [[pluralize]]d):

Trouble; distress; misfortune; adversity.

Examples:

"Music won't solve all the world's ills, but it can make them easier to bear."
Ill as a noun:

Harm or injury.

Examples:

"I wouldn't want you to do me ill."
Ill as a noun:

Evil; moral wrongfulness.
Ill as a noun:

A physical ailment; an illness.

Examples:

"I am incapacitated by rheumatism and other ills."
Ill as a noun (US, slang):

PCP, phencyclidine.

Unwell as an adjective:

Not in good health; not feeling well; somewhat ill

Examples:

"synonyms: ailing under the weather"
Unwell as an adjective (dated, euphemism):

Specifically, ill from menstruation; affected with, or having, catamenial; menstruant.