container vessel vs container ship

container vessel and container ship both are nouns.

Word	Noun	Adjective	Verb	Adverb
container vessel	Yes	No	No	No
container ship	Yes	No	No	No

As nouns, container vessel and container ship are synonyms defined as:

container vessel and container ship: a cargo ship designed to hold containerized cargoes

Other synonyms of container vessel include containership.

container vessel (noun)	container ship (noun)
a cargo ship designed to hold containerized cargoes	a cargo ship designed to hold containerized cargoes