phrenic vein vs vena

phrenic vein and vena both are nouns.

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

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

phrenic vein: either of two veins that drain the diaphragm
vena: a blood vessel that carries blood from the capillaries toward the heart

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

phrenic vein (noun)	vena (noun)
either of two veins that drain the diaphragm	a blood vessel that carries blood from the capillaries toward the heart