ATRESIA
A*tre"si*a, n. Etym: [NL., fr. Gr. (Med.)
Defn: Absence or closure of a natural passage or channel of the body; imperforation.
ATRIAL
A"tri*al, a.
Defn: Of or pertaining to an atrium.
ATRIP A*trip", adv. Etym: [Pref. a- + trip.] (Naut.) (a) Just hove clear of the ground; -said of the anchor. (b) Sheeted home, hoisted taut up and ready for trimming; — said of sails. (c) Hoisted up and ready to be swayed across; — said of yards.
ATRIUM
A"tri*um, n.; pl. Atria. Etym: [L., the fore court of a Roman house.]
1. (Arch.) (a) A square hall lighted from above, into which rooms open at one or more levels. (b) 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.
2. (Anat.)
Defn: The main part of either auricle of the heart as distinct from the auricular appendix. Also, the whole articular portion of the heart.
3. (Zoöl.)