spiderlike vs arachnoid

spiderlike is not a noun while arachnoid is a noun.

Word	Noun	Adjective	Verb	Adverb
spiderlike	No	Yes	No	No
arachnoid	Yes	Yes	No	No

As adjectives, spiderlike and arachnoid are synonyms defined as:

spiderlike and arachnoid: relating to or resembling a member of the class Arachnida

Other synonyms of spiderlike include arachnidian, spiderly, spidery.

spiderlike (noun)	arachnoid (noun)
	air-breathing arthropods characterized by simple eyes and four pairs of legs
	the middle of the 3 meninges

spiderlike (adjective)	arachnoid (adjective)
relating to or resembling a member of the class Arachnida	relating to or resembling a member of the class Arachnida