vena cava vs vena

vena cava and vena both are nouns.

Word	Noun	Adjective	Verb	Adverb
vena cava	Yes	No	No	No
vena	Yes	No	No	No

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

vena cava: either of two large veins that return oxygen-depleted blood to the right atrium of the heart
vena: a blood vessel that carries blood from the capillaries toward the heart

Other hypernyms of vena cava include vein, venous blood vessel.

vena cava (noun)	vena (noun)
either of two large veins that return oxygen-depleted blood to the right atrium of the heart	a blood vessel that carries blood from the capillaries toward the heart