apartment

Why are they called apartments when they are part of the same building?

Obviously this is a matter of perspective. While the individual units may indeed share a wall and a roof, they are nonetheless "apart" from one another in the sense that a tenant cannot access any unit but his own. (Perhaps, then, it is better to think of the tenants as being "apart" from one another, rather than the units themselves.)

From the Latin verb appartare, "to separate."

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