containership vs container vessel

containership and container vessel both are nouns.

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

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

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

Other synonyms of containership include container ship.

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