apartment UK /əˈpɑːt.mənt/US /əˈpɑɹt.mənt/ noun5 •(US, Australia) a home that is only part of a larger building, often one that is rentedI am Jonathan. I am in apartment B4. — I am in apartment C2. — 2016 •A room within a house.For the matter of that, it is difficult to make a nice, genteel sitting-room out of an apartment of which the principal features are a sink and a big gas stove. — 1913 •A conceptual space used for separation in the threading architecture. Objects in one apartment cannot directly access those in another, but must use a proxy. •(no longer used) A suite of rooms within a domicile, designated for a specific person or persons and including a bedroom. •(no longer used) A division of an enclosure that is separate from others; a compartment. formsapartments