[atri.um] n, pl atria also atri.ums [L] (1577) 1: the central room of a Roman house
2. pl usu atriums: a rectangularly shaped open patio around which a house is built; also: a many-storied court in a building (as a hotel) usu. with a skylight 3 [NL, fr. L]: an anatomical cavity or passage; esp: the chamber or either of the chambers of the heart that receives blood from the veins and forces it into the ventricle or ventricles--see heart illustration -- atri.al adj