hemizygous vein vs vena

hemizygous vein and vena both are nouns.

Word	Noun	Adjective	Verb	Adverb
hemizygous vein	Yes	No	No	No
vena	Yes	No	No	No

As nouns, vena is a hypernym of hemizygous vein; that is, vena is a word with a broader meaning than hemizygous vein:

hemizygous vein: a continuation of the left ascending lumbar vein; crosses the midline at the 8th vertebra and empties into the azygos vein
vena: a blood vessel that carries blood from the capillaries toward the heart

Other hypernyms of hemizygous vein include vein, venous blood vessel.

hemizygous vein (noun)	vena (noun)
a continuation of the left ascending lumbar vein; crosses the midline at the 8th vertebra and empties into the azygos vein	a blood vessel that carries blood from the capillaries toward the heart