Synonyms for Arachnoid (same or very similar meaning)
WordNet sense 1 (the middle of the 3 meninges):
arachnoid membraneWordNet sense 2 (relating to or resembling a member of the class Arachnida):
spidery, arachnidian, spiderlike, spiderlyWordNet sense 3 (air-breathing arthropods characterized by simple eyes and four pairs of legs):
arachnidFrom the ODE community, based on WordNetadd/edit