(architecture) A central room or space in ancient Roman homes, open to the sky in the middle; a similar space in other buildings.

plural of atrium

Having an atrium.

One of the chambers of the heart in humans and other mammals, which receives oxygenated blood from the lungs via the pulmonary veins, and pumps it into the left ventricle.

plural of left atrium

(anatomy) The chamber of the heart, in humans and other mammals, that receives deoxygenated blood from the venae cavae and pumps it into the right ventricle.