vena cava vs precava

vena cava and precava both are nouns.

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

As nouns, precava is a hyponym of vena cava; that is, precava 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
precava: receives blood from the head and arms and chest and empties into the right atrium of the heart; formed from the azygos and both brachiocephalic veins

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

vena cava (noun)	precava (noun)
either of two large veins that return oxygen-depleted blood to the right atrium of the heart	receives blood from the head and arms and chest and empties into the right atrium of the heart; formed from the azygos and both brachiocephalic veins