Something such as a door or drawer that is stiff does not move as easily as it should.

If you are stiff, your muscles or joints hurt when you move, because of illness or because of too much exercise.

Stiff can be used to mean difficult or severe.

A stiff drink is a large amount of a strong alcoholic drink.

A stiff wind is blowing quite strongly.

If you are bored stiff, worried stiff, or scared stiff, you are extremely bored, worried, or scared.