atrium

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Architecture A rectangular court, as:
2. n. Architecture A usually skylighted central area, often containing plants, in some modern buildings, especially of a public or commercial nature.
3. n. Architecture The open area in the center of an ancient Roman house.
4. n. Architecture The forecourt of a building, such as an early Christian church, enclosed on three or four sides with porticoes.
5. n. Anatomy A body cavity or chamber, especially either of the upper chambers of the heart that receives blood from the veins and forces it into a ventricle. Also called auricle.

Century Dictionary and Cyclopedia

1. n. In anc. Rom. arch., the entrance-hall, the most important and usually the most splendid apartment of the house. At an early period, and later among the poor, the atrium was used not only as a ceremonial room, but as a reception-room and for general domestic purposes, as cooking and dining. In it were placed the ancestral images and heirlooms, the marriage-couch, the focus or hearth, and generally a small altar. Later, among the wealthy, and when separate apartments were built for kitchen and dining-room, chapel of the lares, etc., it was reserved as a general reception- and show-room. It was lighted by an opening in the roof, called the compluvium, toward which the roof sloped, so as to conduct the rainwater into a cistern in the floor, called the impluvium.
2. n. A hall or court resembling in arrangement an atrium proper, as at the entrance of some classical or early Christian public buildings, etc.
3. n. [NL.] In anatomy, an auricle of the heart, or some equivalent venous cardiac cavity.
4. n. [NL.] In zoology: The chamber or cavity of ascidians, communicating with the exterior, and with the cavity of the alimentary canal. See atrial, and cut under Tunicata.
5. n. A membranous saccular diverticulum of the ear in fishes: as, the atrium sinus imparis, a membranous sac given off from the sinus auditorius impar of fishes, and connected in various ways with the air-bladder.

Wiktionary

1. n. architecture A central room or space in ancient Roman homes, open to the sky in the middle; a similar space in other buildings.
2. n. architecture A square hall lit by daylight from above, into which rooms open at one or more levels.
3. n. anatomy Any enclosed body cavity or chamber
4. n. anatomy An upper chamber of the heart that receives blood from the veins and forces it into a ventricle. In higher vertebrates, the right atrium receives blood from the superior vena cava and inferior vena cava, and the left atrium receives blood from the left and right pulmonary veins.
5. n. anatomy A microscopic air sac within a pulmonary alveolus.
6. n. palynology A cavity inside a porate aperture of a pollen grain formed by the separation of the sexine and nexine layers, widening toward the interior of the grain.

GNU Webster's 1913

1. n. A square hall lighted from above, into which rooms open at one or more levels.
2. n. An open court with a porch or gallery around three or more sides; especially at the entrance of a basilica or other church. The name was extended in the Middle Ages to the open churchyard or cemetery.
3. n. (Anat.) The main part of either auricle of the heart as distinct from the auricular appendix. Also, the whole articular portion of the heart.
4. n. (Zoöl.) A cavity in ascidians into which the intestine and generative ducts open, and which also receives the water from the gills. See Ascidioidea.
5. n. (Anat.) A cavity, entrance, or passage

WordNet 3.0

1. n. the central area in a building; open to the sky
2. n. any chamber that is connected to other chambers or passageways (especially one of the two upper chambers of the heart)