from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The first chamber in the heart of fish, amphibians, and reptiles, which receives blood from the veins and contracts to force the blood into the atrium.
from the GNU version of the Collaborative International Dictionary of English
- n. In the lower vertebrates, a distinct chamber of the heart formed by the union of the large systematic veins and opening into the auricle.
New Latin sinus vēnōsus : Medieval Latin sinus, sinus + Latin vēnōsus, venous.(American Heritage® Dictionary of the English Language, Fourth Edition)