1640s, "private rooms for the use of one person within a house," from French appartement (16c.), from Italian appartimento, literally "a separated place," from appartere "to separate," from a "to" (see ad-) + parte "side, place," from Latin partem (see part, n.). Sense of "set of private rooms in a building entirely of these" (the U.S. equivalent of British flat) is first attested 1874.