I. ə-ˈrak-ˌnȯid adjective
Date: 1789
1. : of or relating to a thin membrane of the brain and spinal cord that lies between the dura mater and the pia mater
2. : covered with or composed of soft loose hairs or fibers
II. noun
Etymology: New Latin arachnoides, from Greek arachnoeidēs, like a cobweb, from arachnē spiderweb
Date: circa 1847
: an arachnoid membrane
III. adjective
Etymology: New Latin Arachn ida + English -oid
Date: 1852
: resembling or related to the arachnids