rectal vein vs vena

rectal vein and vena both are nouns.

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

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

rectal vein: any of several veins draining the walls of the anal canal and rectum
vena: a blood vessel that carries blood from the capillaries toward the heart

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

rectal vein (noun)	vena (noun)
any of several veins draining the walls of the anal canal and rectum	a blood vessel that carries blood from the capillaries toward the heart