man-of-war vs combat ship

man-of-war and combat ship both are nouns.

Word	Noun	Adjective	Verb	Adverb
man-of-war	Yes	No	No	No
combat ship	Yes	No	No	No

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

Other hypernyms of man-of-war include war vessel, warship.

man-of-war (noun)	combat ship (noun)
large siphonophore having a bladderlike float and stinging tentacles	a government ship that is available for waging war
a warship intended for combat