Where does “arachnoid” come from?

Arachnoid comes from Ancient Greek ἀράχνη, meaning spider or spider's web.

arachnoid (English): Relating to or resembling spiders; Relating to or...

Definitions

Step	Language	Word	Meaning
1	New Latin	arachnoīdēs	—
2	Ancient Greek	ᾰ̓ρᾰχνοειδής	—
3	Ancient Greek	-ειδής	like, connected to, from the nature of, full of;...
4	Ancient Greek	-ής	adjective suffix
5	Proto-Indo-European	-ēs	Primarily forms adjectival bahuvrīhi compounds
6	Proto-Indo-European	-ess	—
7	Proto-Indo-European	-os	Creates action nouns or result nouns from verbs;...