The difference between Sick and Unwell

When used as adjectives, sick means having an urge to vomit, whereas unwell means not in good health.

Sick is also noun with the meaning: sick people in general as a group.

Sick is also verb with the meaning: to vomit.

check bellow for the other definitions of Sick and Unwell

Sick as an adjective:

Having an urge to vomit.
Sick as an adjective (chiefly, American):

In poor health.

Examples:

"She was sick all day with the flu."
Sick as an adjective (colloquial):

Mentally unstable, disturbed.
Sick as an adjective (colloquial):

In bad taste.

Examples:

"That's a sick joke."
Sick as an adjective:

Tired of or annoyed by something.

Examples:

"I've heard that song on the radio so many times that I'm starting to get sick of it."
Sick as an adjective (slang):

Very good, excellent, awesome, badass.

Examples:

"This tune is sick."

"Dude, this car's got a sick subwoofer!"
Sick as an adjective:

In poor condition.

Examples:

"'sick building syndrome; my car is looking pretty sick; my job prospects are pretty sick'"
Sick as an adjective (agriculture):

Failing to sustain adequate harvests of crop, usually specified.

Sick as a noun:

Sick people in general as a group.

Examples:

"We have to cure the sick."
Sick as a noun (British, colloquial):

vomit.

Examples:

"He lay there in a pool of his own sick."

Sick as a verb:

To vomit.

Examples:

"I woke up at 4 am and sicked on the floor."
Sick as a verb (obsolete, intransitive):

To fall sick; to sicken.

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.