Azygos

In anatomy, azygos, from the Greek άνισος, refers to a structure that is unpaired. This is relatively unusual, as most elements of anatomy reflect bilateral symmetry. Another term for the same concept is impar.

Well-known structures incorporating this nomenclature include the azygos vein and ganglion impar.

Also azygos lobe, refers to a normal variant shown in the right upper medial lung