Ill means sick or unwell. When you're ill, your body isn't working the way it should: you might have a fever, feel nauseous, or lack energy. Someone who catches the flu is ill until they recover. A student home ill with a cold is too sick to go to school.

The word also describes things that are bad or harmful. Ill effects are negative consequences, like the ill effects of staying up too late on a school night. An ill wind brings bad fortune. When someone speaks ill of another person, they say mean or critical things about them.

You'll also see ill in phrases that describe unfortunate situations. Ill-fated means doomed to fail or end badly, like an ill-fated expedition to the Arctic. Something done with ill will is done with unfriendly or even hostile intentions. If something bodes ill, it suggests trouble ahead.

Notice how the word carries a sense of something being wrong, whether it's your health, someone's intentions, or how a situation might turn out. The opposite would be well: feeling well instead of ill, speaking well of someone instead of speaking ill of someone, or a situation turning out well instead of ill.