conjunctival veins vs vena

conjunctival veins and vena both are nouns.

Word	Noun	Adjective	Verb	Adverb
conjunctival veins	Yes	No	No	No
vena	Yes	No	No	No

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

conjunctival veins: veins draining the conjunctiva
vena: a blood vessel that carries blood from the capillaries toward the heart

Other hypernyms of conjunctival veins include vein, venous blood vessel.

conjunctival veins (noun)	vena (noun)
veins draining the conjunctiva	a blood vessel that carries blood from the capillaries toward the heart