war vessel vs warship

war vessel and warship both are nouns.

Word	Noun	Adjective	Verb	Adverb
war vessel	Yes	No	No	No
warship	Yes	No	No	No

As nouns, war vessel and warship are synonyms defined as:

war vessel and warship: a government ship that is available for waging war

Other synonyms of war vessel include combat ship.

war vessel (noun)	warship (noun)
a government ship that is available for waging war	a government ship that is available for waging war