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architecture.

also called cavaedium. the main or central room of an ancient roman house, open to the sky at the center and usually having a pool for the collection of rain water.
a courtyard, flanked or surrounded by porticoes, in front of an early or medieval christian church.
a skylit central court in a contemporary building or house.

anatomy. either of the two upper chambers on each side of the heart that receive blood from the veins and in turn force it into the ventricles.
historical examples

the two atrial tubes of each zooid remain separate in front but unite posteriorly.
the works of francis maitland balfour, volume iii (of 4) francis maitland balfour

during the above described processes the test remains quite intact, and is not perforated at the oral or the atrial openings.
the works of francis maitland balfour, volume iii (of 4) francis maitland balfour

the oral opening into the branchial sack is directed upwards: an atrial opening is remarkably enough not present.
the works of francis maitland balfour, volume iii (of 4) francis maitland balfour

it contains the whole of the nervous system (ng), which is covered behind by the opening of the atrial tubes (cl).
the works of francis maitland balfour, volume iii (of 4) francis maitland balfour

the atrial cavities in pyrosoma are clearly lined by epiblast, just as in simple ascidians.
the works of francis maitland balfour, volume iii (of 4) francis maitland balfour

when the young colony is ready to become free, it escapes from the atrial cavity of the parent, and increases in size by budding.
the works of francis maitland balfour, volume iii (of 4) francis maitland balfour

the nervous system is shewn at n, and at points to an atrial tube.
the works of francis maitland balfour, volume iii (of 4) francis maitland balfour

the gills lead also, as in ascidians, to another cavity, the atrial chamber.
stories of the universe: animal life b. lindsay

from the atrial chamber the water flows out into the external world.
a guide to the study of fishes, volume 1 (of 2) david starr jordan

in teleutoscolex there is but one pair of funnels opening into the same segment with the atrial pore.
earthworms and their allies frank e. beddard

noun (pl) atria (ˈeɪtrɪə; ˈɑː-)
the open main court of a roman house
a central often gl-ss-roofed hall that extends through several storeys in a building, such as a shopping centre or hotel
a court in front of an early christian or medieval church, esp one flanked by colonnades
(anatomy) a cavity or chamber in the body, esp the upper chamber of each half of the heart
adj.

by 1860 in the medical sense, from atrium + -al (1).
n.

1570s, from latin atrium “central court or main room of an ancient roman house, room which contains the hearth,” sometimes said (on authority of varro, “de lingua latina”) to be an etruscan word, but perhaps from pie -ater- “fire,” on notion of “place where smoke from the hearth escapes” (through a hole in the roof). anatomical sense of “either of the upper cavities of the heart” first recorded 1870. meaning “skylit central court in a public building” first attested 1967.

atrial a·tri·al (ā’trē-əl)
adj.
of or relating to an atrium.

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 p-ssageways 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.

atrium
(ā’trē-əm)
plural atria or atriums
a chamber of the heart that receives blood from the veins and forces it by muscular contraction into a ventricle. mammals, birds, reptiles, and amphibians have two atria; fish have one.