from
The Collaborative International Dictionary of English v.0.48
Apartment house \A*part"ment house\
A building comprising a number of lving units (apartments[4])
designed for separate housekeeping tenements, but having
conveniences, such as heat, light, elevator service, etc.,
furnished in common; contrasted to a {detached dwelling}.
Sometimes distinguished in the United States from a {flat
house}, in which each living unit comprises one entire floor,
whereas in an apartment house a floor may be partitioned into
any number of apartments[4].
[Webster 1913 Suppl. +PJC]