arachnoid

arachnoid · adjective, noun¹

1. Ancient Greek · derived fromᾰ̓ρᾰχνοειδής“like a cobweb”
2. New Latin · borrowed fromarachnoīdēs
3. English todayarachnoid

Mid 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.

arachnoid · adjective, noun²

19th century from taxonomic name Arachnida + -oid.