The difference between Ill and Under the weather

When used as adjectives, ill means evil, whereas under the weather means somewhat ill or gloomy.

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 Under the weather

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.

Under the weather as an adjective (idiomatic):

Somewhat ill or gloomy.
Under the weather as an adjective (idiomatic):

Somewhat intoxicated or suffering from a hangover.
Under the weather as an adjective (idiomatic, obsolete):

Experiencing adversity.