container ship vs container vessel

container ship and container vessel both are nouns.

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

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

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

Other synonyms of container ship include containership.

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