man-of-war vs jellyfish

man-of-war and jellyfish both are nouns.

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

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

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

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

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