[arach.noid] adj (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
[2]arachnoid n [NL arachnoides, fr. Gk arachnoeides, like a cobweb, fr. arachne spider, spider's web] (ca. 1847): an arachnoid membrane [3]arachnoid adj [NL Arachnida + E -oid] (1852): resembling or related to the arachnids