eye cup vs vessel

eye cup and vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
eye cup	Yes	No	No	No
vessel	Yes	No	No	No

As nouns, vessel is a hypernym of eye cup; that is, vessel is a word with a broader meaning than eye cup:

eye cup: a small vessel with a rim curved to fit the orbit of the eye; use to apply medicated or cleansing solution to the eyeball
vessel: an object used as a container (especially for liquids)

eye cup (noun)	vessel (noun)
a small vessel with a rim curved to fit the orbit of the eye; use to apply medicated or cleansing solution to the eyeball	a craft designed for water transportation
	an object used as a container (especially for liquids)
	a tube in which a body fluid circulates