Single, not one of a pair.
The term “azygous” refers to the absence of a pairing or a structure that lacks a corresponding organ on the opposite side of the body. It is commonly used to describe certain organs, such as the heart, which do not have a twin organ on the opposite side. In the context of anatomy, the azygous vein is responsible for draining blood from the abdomen and chest, and it courses along the right side of the spine. Understanding the concept of azygous helps in comprehending the unique anatomical features and characteristics of certain structures in the human body.