- (intransitive) To assume a sitting position from a position lying down.
- Despite being sick, Lorin sat up to greet the visitors.
- 1900, L. Frank Baum, The Wonderful Wizard of Oz
- She was awakened by a shock, so sudden and severe that if Dorothy had not been lying on the soft bed she might have been hurt. As it was, the jar made her catch her breath and wonder what had happened; and Toto put his cold little nose into her face and whined dismally. Dorothy sat up and noticed that the house was not moving; nor was it dark, for the bright sunshine came in at the window, flooding the little room. She sprang from her bed and with Toto at her heels ran and opened the door.
- (intransitive) To sit erect.
- Sit up straight, mister!
- (intransitive) To show sudden interest or surprise.
- He sat up when we mentioned the increased pay package.
- (chiefly, sport, 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.
sit up (plural sit ups)
- Alternative spelling of sit-up; Alternative spelling of situp