mid-14c., "to take possession of," also "to take up space or time, employ (someone)," irregularly borrowed from Old French occuper "occupy (a person or place), hold, seize" (13c.) or directly from Latin occupare "take over, seize, take into possession, possess, occupy," from ob "over" (see ob-) + intensive form of capere "to grasp, seize" (see capable). The final syllable of the English word is difficult to explain, but it is as old as the record; perhaps from a modification made in Anglo-French. During 16c.-17c. a common euphemism for "have sexual intercourse with" (sense attested from early 15c.), which caused it to fall from polite usage.
Related: Occupied; occupying.