What is "hunt's-up"

Hunt's-up \Hunt's"-up`\, n. A tune played on the horn very early in the morning to call out the hunters; hence, any arousing sound or call. [Obs.]
--Shak.

Time plays the hunt's-up to thy sleepy head.
--Drayton.

n. (context obsolete English) A tune played on the horn very early in the morning to call out the hunters; hence, any rousing sound or call.