c.1300, "container," from Old French vessel (French vaisseau) from Latin vascellum "small vase or urn," also "a ship," diminutive of vasculum, itself a diminutive of vas "vessel." Sense of "ship, boat" is found in English c.1300. "The association between hollow utensils and boats appears in all languages" [Weekley]. Meaning "canal or duct of the body" (especially for carrying blood) is attested from late 14c.
vessel ves·sel (věs'əl)
A duct, canal, or other tube that contains or conveys a body fluid such as blood or lymph.