Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
Wiktionary
n. (alternative form of sunup English)
Wikipedia
Sun-Up is a 1925 drama film directed by Edmund Goulding based upon a successful 1924 play by Lula Vollmer. The film stars Lucille La Verne, replaying her successful New York stage role, Pauline Starke and Conrad Nagel.
Usage examples of "sun-up".
My horse-wrangler had made arrangements with the cook to look after his charges, and in anticipation of the day before him, had our mounts corralled before sun-up.
Wolf Creek below, and orders were given to bring along every possible man from the local outfits and to meet at the rendezvous within an hour after sun-up the next morning.
He sat down, the first chance he'd had to do that since sun-up, and leaped to his feet again as the multitool he'd stowed in his cargo pocket clanged against the frame of the seat.