sit%20up

To assume a sitting position from a position lying down.

“Despite being sick, Lorin sat up to greet the visitors.”

To sit erect.

“Sit up straight, mister!”

To show sudden interest or surprise.

“He sat up when we mentioned the increased pay package.”

(of the ball) To bounce, especially to a comfortable height.

To not go to bed (notionally remaining in a sitting position).

“I sat up all night waiting for her to come home.”

An exercise in which the abdominal muscles are contracted, bringing the torso of a person lying down to a more upright position.

“Susan's doing sit-ups to strengthen her muscles.”