crinoid vs feather star

crinoid and feather star both are nouns.

Word	Noun	Adjective	Verb	Adverb
crinoid	Yes	Yes	No	No
feather star	Yes	No	No	No

As nouns, feather star is a hyponym of crinoid; that is, feather star is a word with a more specific, narrower meaning than crinoid:

crinoid: primitive echinoderms having five or more feathery arms radiating from a central disk
feather star: free-swimming stalkless crinoid with ten feathery arms; found on muddy sea bottoms

Other hyponyms of crinoid include sea lily, comatulid.

crinoid (noun)	feather star (noun)
primitive echinoderms having five or more feathery arms radiating from a central disk	free-swimming stalkless crinoid with ten feathery arms; found on muddy sea bottoms

crinoid (adjective)	feather star (adjective)
of or relating to or belonging to the class Crinoidea