arachnid vs arthropod

arachnid and arthropod both are nouns.

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

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

arachnid: 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

arachnid (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