cnidarian vs jellyfish

cnidarian and jellyfish both are nouns.

Word	Noun	Adjective	Verb	Adverb
cnidarian	Yes	No	No	No
jellyfish	Yes	No	No	No

As nouns, jellyfish is a hyponym of cnidarian; that is, jellyfish is a word with a more specific, narrower meaning than cnidarian:

cnidarian: radially symmetrical animals having saclike bodies with only one opening and tentacles with stinging structures; they occur in polyp and medusa forms
jellyfish: any of numerous usually marine and free-swimming coelenterates that constitute the sexually reproductive forms of hydrozoans and scyphozoans

Other hyponyms of cnidarian include polyp, medusa, medusan, medusoid, scyphozoan, hydroid, hydrozoan, actinozoan, anthozoan.

cnidarian (noun)	jellyfish (noun)
radially symmetrical animals having saclike bodies with only one opening and tentacles with stinging structures; they occur in polyp and medusa forms	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