WHOA it's been a long time since I did one of these. But you know what? I'm doing one today. And it's a doozy. Are you ready for this?
According to www.etymonline.com, the origin of the word apartment is as follows:
"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" (see ad-) + parte "side, place," from L. partem (see part). Sense of "set of private rooms in a building entirely of these" (the U.S. equivalent of British flat) is first attested 1874."
So now when someone pulls that old joke about "Why do they call them apartments when they're all stuck together?" you can answer with your new smarts. "Actually, the word apartment dates back to . . . "