01 n. A square hall lighted from above, into which rooms open at one or more levels.
pl.
Atria
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1.
A square hall lighted from above, into which rooms open at one or more levels.(Arch.)
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2.
The main part of either auricle of the heart as distinct from the auricular appendix. Also, the whole articular portion of the heart.(Anat.)
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3.
A cavity in ascidians into which the intestine and generative ducts open, and which also receives the water from the gills. See Ascidioidea.(Zool.) See: Ascidioidea
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4.
A cavity, entrance, or passage; as, the atrium, or atrial cavity, in the body wall of the amphioxus; an atrium of the infundibula of the lungs, etc.(Anat.)