proper name of the island containing England, Scotland, and Wales, c. 1300, Breteyne, from Old French Bretaigne, from Latin Britannia, earlier Brittania, from Brittani "the Britons" (see Briton). The Old English place-name Brytenlond meant "Wales." If there was a Celtic name for the island, it has not been recorded.
1530s (late 15c. as a Latin word in English), originally a stage direction, from Latin exit "he or she goes out," third person singular present indicative of exire "go out, go forth, depart," from ex- "out" (see ex-) + ire "to go" (from PIE root *ei- "to go"). Also from Latin exitus "a leaving, a going out," noun of action from exire.
Meaning "a departure" (originally from the stage) is from 1580s. Meaning "a way of departure" is from 1690s; specific meaning "door for leaving" is from 1786. The verb is c. 1600, from the noun; it ought to be left to stage directions and the clunky jargon of police reports. Related: Exited; exiting.
Those who neither know Latin nor read plays are apt to forget or not know that this is a singular verb with plural exeunt. [Fowler]