Someone who is ill is suffering from a disease or a health problem.

Difficulties and problems are sometimes referred to as ills .

Ill is evil or harm.

Ill means the same as 'badly'.

You can use ill in front of some nouns to indicate that you are referring to something harmful or unpleasant.

If you say that someone can ill afford to do something, or can ill afford something, you mean that they must prevent it from happening because it would be harmful or embarrassing to them.

If something bodes ill or augurs ill, it gives you a reason to fear that something harmful might happen soon.

If you fall ill or are taken ill, you suddenly become ill.

If you say that something is happening or will happen for good or ill, you mean that it is out of anyone's control whether it happens and what its effects will be.