arachnoid vs arthropod

arachnoid and arthropod both are nouns.

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

As nouns, arthropod is a hypernym of arachnoid; that is, arthropod is a word with a broader meaning than arachnoid:

arachnoid: air-breathing arthropods characterized by simple eyes and four pairs of legs
arthropod: invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin

arachnoid (noun)	arthropod (noun)
air-breathing arthropods characterized by simple eyes and four pairs of legs	invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin
the middle of the 3 meninges

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