sit-up

(noun) a stomach exercise in which a person sits up from a supine position without using the arms for leverage.

(verb) not go to bed. Synonyms: stay up, sit up. Examples: "Don't stay up so late--you have to go to work tomorrow." "We sat up all night to watch the election."

(verb) change to an upright sitting position. Synonyms: sit up. Example: "He sat up in bed."