Nouns

(n)arachnoid, arachnoid membranethe middle of the 3 meninges
(n)arachnid, arachnoidair-breathing arthropods characterized by simple eyes and four pairs of legs

Adjectives

(a)arachnoid, arachnidian, spidery, spiderlike, spiderlyrelating to or resembling a member of the class Arachnida