jellyfish vs man-of-war

jellyfish and man-of-war both are nouns.

Word	Noun	Adjective	Verb	Adverb
jellyfish	Yes	No	No	No
man-of-war	Yes	No	No	No

As nouns, jellyfish and man-of-war are synonyms defined as:

jellyfish and man-of-war: large siphonophore having a bladderlike float and stinging tentacles

Other synonyms of jellyfish include Portuguese man-of-war.

jellyfish (noun)	man-of-war (noun)
any of numerous usually marine and free-swimming coelenterates that constitute the sexually reproductive forms of hydrozoans and scyphozoans	large siphonophore having a bladderlike float and stinging tentacles
large siphonophore having a bladderlike float and stinging tentacles	a warship intended for combat