brachiocephalic vein vs vena

brachiocephalic vein and vena both are nouns.

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

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

brachiocephalic vein: veins formed by the union of the internal jugular and subclavian veins
vena: a blood vessel that carries blood from the capillaries toward the heart

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

brachiocephalic vein (noun)	vena (noun)
veins formed by the union of the internal jugular and subclavian veins	a blood vessel that carries blood from the capillaries toward the heart