venula vs vena

venula and vena both are nouns.

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

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

venula: a minute vein continuous with a capillary
vena: a blood vessel that carries blood from the capillaries toward the heart

Other hypernyms of venula include vein, venous blood vessel.

venula (noun)	vena (noun)
a minute vein continuous with a capillary	a blood vessel that carries blood from the capillaries toward the heart