cestode vs flatworm

cestode and flatworm both are nouns.

Word	Noun	Adjective	Verb	Adverb
cestode	Yes	No	No	No
flatworm	Yes	No	No	No

As nouns, flatworm is a hypernym of cestode; that is, flatworm is a word with a broader meaning than cestode:

cestode: ribbonlike flatworms that are parasitic in the intestines of humans and other vertebrates
flatworm: parasitic or free-living worms having a flattened body

Other hypernyms of cestode include platyhelminth.

cestode (noun)	flatworm (noun)
ribbonlike flatworms that are parasitic in the intestines of humans and other vertebrates	parasitic or free-living worms having a flattened body