noun the arachnoid membrane.
2. arachnoid ·noun one of the arachnoidea.
3. arachnoid ·adj resembling a spider's web; cobweblike.
4. arachnoid ·adj covered with, or composed of, soft, loose hairs or fibers, so as to resemble a cobweb; cobwebby.
5. arachnoid ·adj pertaining to a thin membrane of the brain and spinal cord, between the dura mater and pia mater.