emissary vein vs vena

emissary vein and vena both are nouns.

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

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

emissary vein: one of several connecting veins in the scalp and head that drain blood from sinuses in the dura mater to veins outside the skull
vena: a blood vessel that carries blood from the capillaries toward the heart

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

emissary vein (noun)	vena (noun)
one of several connecting veins in the scalp and head that drain blood from sinuses in the dura mater to veins outside the skull	a blood vessel that carries blood from the capillaries toward the heart