a. and sb. [ad. mod.L. arachnoīdes, a. Gr. ἀραχνο-ειδής cobweb-like: see -OID.] A. adj.
1. Bot. Covered with or formed of long, delicate, cobweb-like hairs or fibers.
1857. Berkeley, Cryptog. Bot., § 401. An arachnoid or woven veil attached to the edge, and sometimes entirely covering the gills.
1874. M. Cooke, Fungi, 91. Arachnoid threads.
2. Phys. Of or pertaining to the arachnoid. (See B.)
1836–9. Todd, Cycl. Anat. & Phys., II. 278/1. The chamber is lined by the arachnoid membrane.
1872. Huxley, Phys., xi. 249. It secretes … the arachnoid fluid.
3. Ent. Resembling the Arachnida.
1852. Dana, Crust., I. 14. The Arachnoid type, as in Nymphon.
B. sb. The delicate serous membrane or membranous sac lining the dura mater, and enveloping the brain and spinal cord.
[1751. Chambers, Cycl., Arachnoides … a fine, thin, transparent membrane … supposed to invest the whole substance of the brain, medulla oblongata, and spinal marrow.]
1839–47. Todd, Cycl. Anat. & Phys., III. 638/1. The arachnoid covers the superior surface of the cerebellum.
