The difference and usage between ill and sick

When ill means "sick; sick", it is generally used as a predicate and not as an attributive; while sick can be used as both a predicate and an attributive. For example, "patient" can be said a sick man or the sick, but not an ill man or the ill. Another example: She is ill / sick in bed. She is ill in bed. She is looking after her sick father. She is looking after her sick father.

Sick means "disgusting; boring". Such as: The smell makes me sick. The smell makes me feel sick.

ill means "bad; evil" when used as an attributive to modify a noun. Such as: He is an ill man. He is an evil person.