1640s, "private rooms for the use of one person within a house," from Fr. appartement
(16c.), from It. appartimento
, lit. "a separated place," from appartere
"to separate," from a
"to" + parte
"side, place," from L. partem
). Sense of "set of private rooms in a building entirely of these" (the U.S. equivalent of British flat
) is first attested 1874.