Meaning

noun the middle of the 3 meninges

noun air-breathing arthropods characterized by simple eyes and four pairs of legs

adjective relating to or resembling a member of the class Arachnida

originMid 18th century borrowing from New Latin arachnoīdēs, from Ancient Greek ᾰ̓ρᾰχνοειδής (ărăkhnoeidḗs, “like a cobweb”), from ᾰ̓ρᾰ́χνη (ărắkhnē, “spider web”) + -ο- (-o-) + -ειδής (-eidḗs, “-oid, -like”). By surface analysis, arachn- + -oid.

Etymology from Wiktionary, CC BY-SA 3.0