sit up

Verb

sit up (third-person singular simple present sits up, present participle sitting up, simple past and past participle sat up)

1. (intransitive) To assume a sitting position from a position lying down.
   • Despite being cancer-ridden, Lorin sat up to greet the visitors.
   • 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...1900 May 17, L[yman] Frank Baum, The Wonderful Wizard of Oz, Chicago, Ill.; New York, N.Y.: Geo[rge] M[elvin] Hill Co., →OCLC
2. (intransitive) To sit erect.
   • Sit up straight, mister!
3. (intransitive) To show sudden interest or surprise.
   • He sat up when we mentioned the increased pay package.
4. To bounce, especially to a comfortable height.
   • And within five minutes of the change United were level. Gabriel Obertan tuned his marker inside out and delivered a cross from the right that hit Hernandez and sat up perfectly for Owen to nod home.2011 January 29, Ian Hughes, “Southampton 1 - 2 Man Utd”, in BBC
5. To not go to bed (notionally remaining in a sitting position).
   • I sat up all night waiting for her to come home.
6. To stop pedalling hard.
   • Half way up the climb, Jones sat up and let Smith continue alone.
7. (India, historical) For a young lady to open her house for several successive nights for any visitors who wish to pay their respects.