cruiser vs combat ship

cruiser and combat ship both are nouns.

Word	Noun	Adjective	Verb	Adverb
cruiser	Yes	No	No	No
combat ship	Yes	No	No	No

As nouns, combat ship is a hypernym of cruiser; that is, combat ship is a word with a broader meaning than cruiser:

cruiser: a large fast warship; smaller than a battleship and larger than a destroyer
combat ship: a government ship that is available for waging war

Other hypernyms of cruiser include war vessel, warship.

cruiser (noun)	combat ship (noun)
a large fast warship; smaller than a battleship and larger than a destroyer	a government ship that is available for waging war
a large motorboat that has a cabin and plumbing and other conveniences necessary for living on board
a car in which policemen cruise the streets; equipped with radiotelephonic communications to headquarters