azygos vein: 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
entity: that which is perceived or known or inferred to have its own distinct existence (living or nonliving)
hypervitaminosis: an abnormal condition resulting from taking vitamins excessively; can be serious for vitamins A or D or K