half-holiday

Half of a working or school day set aside for recreation on a special occasion.

1784, obituary of Daniel Wray in The Gentleman’s Magazine, Volume 54, Part 1, p. 72, His memory is still reflected on with a degree of pleasure by some […] who can revive the long-buried ideas of what passed at that school about the year 1716 or 17; when Sir Daniel was always ready, if any body was wanted, to beg a half-holiday on Tuesday afternoons.

Mr. Pecksniff and Mr. Jinkins came home to dinner, arm-in-arm; for the latter gentleman had made half-holiday, on purpose; thus gaining an immense advantage over the youngest gentleman and the rest, whose time, as it perversely chanced, was all bespoke, until the evening.

A religious festival lasting for half a day.

For they had […] some appointed times, appropriated to the worship of their severall gods, as before was shewed: their holydayes, & half-holydayes, according to that estimation which their gods had gotten in the World.

But this [Carmentalia] was an half holiday, (intercisus); for after mid day it was dies profestus, a common work day.