Source : Webster's Revised Unabridged Dictionary (1913)

Arachnoid \A*rach"noid\, n.
   1. (Anat.) The arachnoid membrane.

   2. (Zo["o]l.) One of the Arachnoidea.

Arachnoid \A*rach"noid\, a. [Gr. ? like a cobweb; ? spider,
   spider's web + ? form.]
   1. Resembling a spider's web; cobweblike.

   2. (Anat.) Pertaining to a thin membrane of the brain and
      spinal cord, between the dura mater and pia mater.

   3. (Bot.) Covered with, or composed of, soft, loose hairs or
      fibers, so as to resemble a cobweb; cobwebby.

Source : WordNet®

arachnoid
     adj : relating to or resembling a member of the class Arachnida
           [syn: {arachnidian}, {spidery}, {spiderlike}, {spiderly}]

arachnoid
     n 1: the middle of the 3 meninges [syn: {arachnoid membrane}]
     2: air-breathing arthropods characterized by simple eyes and
        four pairs of legs [syn: {arachnid}]