What is the synonym for sick?

The noun form for the adjective ill is illness. The Word ill is also a noun, a Word for a problem or difficulty; people in general who are ill.

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The Word 'ill' is a noun, a singular, common, abstract noun:

• We don't wish them ill.
• The ills of modern society can't be cured by simple answers.
• There is very little public policy to support the mentally ill.

The Word 'ill' is an adverb:

• The public was ill advised of the situation.

The Word 'ill' is an adjective:

• The ill passengers were taken to the nearest airport to receive care.