atrium a·tri·um (ā'trē-əm)
n. pl. a·tri·ums or a·tri·a (ā'trē-ə)
A chamber or cavity to which several chambers or passageways are connected.
Either the right or the left upper chamber of the heart that receives blood from the veins and forces it into a ventricle.
That part of the tympanic cavity that lies below the eardrum.
A subdivision of the alveolar duct in the lung from which the alveolar sacs open.