vessel vs blood vessel

vessel and blood vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
vessel	Yes	No	No	No
blood vessel	Yes	No	No	No

As nouns, blood vessel is a hyponym of vessel; that is, blood vessel is a word with a more specific, narrower meaning than vessel:

vessel (noun)	blood vessel (noun)
a craft designed for water transportation	a vessel in which blood circulates
an object used as a container (especially for liquids)
a tube in which a body fluid circulates