vena cava vs postcava

vena cava and postcava both are nouns.

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

As nouns, postcava is a hyponym of vena cava; that is, postcava is a word with a more specific, narrower meaning than vena cava:

vena cava: either of two large veins that return oxygen-depleted blood to the right atrium of the heart
postcava: receives blood from lower limbs and abdominal organs and empties into the posterior part of the right atrium of the heart; formed from the union of the two iliac veins

Other hyponyms of vena cava include inferior vena cava, precava, superior vena cava.

vena cava (noun)	postcava (noun)
either of two large veins that return oxygen-depleted blood to the right atrium of the heart	receives blood from lower limbs and abdominal organs and empties into the posterior part of the right atrium of the heart; formed from the union of the two iliac veins