Wiktionary
vb. 1 To remain awake, to not go to bed. 2 To maintain an erection.
WordNet
v. not go to bed; "Don't stay up so late--you have to go to work tomorrow"; "We sat up all night to watch the election" [syn: sit up]
Usage examples of "stay up".
My father frequently had business dinners, and we were allowed to stay up until he got home.
Now THAT is a cool operating system, and if such a thing were actually made available on the Internet (for free, of course) every hacker in the world would download it right away and then stay up all night long messing with it, spitting out universes right and left.
And a Climber often had to stay up for days while enemy warships hunted her.
If his grades don't go up and stay up, he may give up and resort to playing again.
You happen to be protected by the Paradox of Transit Displacement, as long as you stay up the line.
For several decades now, the great state of Wisconsin had taken tax money from the other states so that the price they paid for milk would stay up.
He was hungry, the kind of gnawing, stomach-talking hunger he had felt only during the happiest moments of his life, the years at the University when he and Kishkin would stay up the entire night studying for exams, continually eating sausages and hard-boiled eggs.