venous blood system vs venation

venous blood system and venation both are nouns.

Word	Noun	Adjective	Verb	Adverb
venous blood system	Yes	No	No	No
venation	Yes	No	No	No

As nouns, venous blood system and venation are synonyms defined as:

venous blood system and venation: (zoology) the system of venous blood vessels in an animal

venous blood system (noun)	venation (noun)
(zoology) the system of venous blood vessels in an animal	(zoology) the system of venous blood vessels in an animal
	(botany) the arrangement of veins in a leaf