intransitive verb Date: 13th century 1. to rise from a lying to a sitting position, to sit with the back erect, to show interest, alertness, or surprise , to stay up after the usual time for going to bed
SIT UP
Meaning of SIT UP in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012