The azygos vein is a prominent vein in the human body that is responsible for carrying blood from the lower and middle parts of the body. There are a few synonyms that can be used to refer to the azygos vein, depending on the context in which it is being discussed. Some of these synonyms include unpaired vein, single vein, or solus vein. Additionally, the azygos vein is sometimes referred to as the Hemiazygos vein, which is the name of its lateral counterpart. Although these terms may not be as commonly used as azygos vein, they can provide more options for describing this important vein in the circulatory system.