Definitions for azygos vein
azygos vein, azygous vein, vena azygos(noun)
one of a system of veins that drain the thoracic and abdominal walls; arises as a continuation of the right ascending lumbar vein and terminates in the superior vena cava
U.S. National Library of Medicine
A vein which arises from the right ascending lumbar vein or the vena cava, enters the thorax through the aortic orifice in the diaphragm, and terminates in the superior vena cava.