Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • adj. Anatomy Of or relating to a delicate membrane enclosing the spinal cord and brain.
  • adj. Of, relating to, or resembling arachnids.
  • adj. Covered with or consisting of thin, soft, entangled hairs or fibers resembling those of a cobweb or spider's web.
  • n. See arachnid.
  • n. Anatomy A delicate membrane that encloses the spinal cord and brain and lies between the pia mater and dura mater.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. Relating to spiders.
  • adj. Relating to or resembling spider webs.
  • adj. Relating to the arachnoid mater, the middle layer of the meninges, the three membranes that protect the brain.
  • n. An arachnid
  • n. The arachnoid mater, the middle layer of the meninges, the three membranes that protect the brain
  • n. A round network of fractures in the crust of Venus

from the GNU version of the Collaborative International Dictionary of English

  • adj. Resembling a spider's web; cobweblike.
  • adj. Pertaining to a thin membrane of the brain and spinal cord, between the dura mater and pia mater.
  • adj. Covered with, or composed of, soft, loose hairs or fibers, so as to resemble a cobweb; cobwebby.
  • n. The arachnoid membrane.
  • n. One of the Arachnoidea.

from The Century Dictionary and Cyclopedia

  • Of or pertaining to the Arachnida; arachnidan.
  • Like or likened to a cobweb: applied, in anatomy— to the arachnoid of the brain (see II.);
  • to the hyaloid membrane or arachnoid of the eye (see II.).
  • n. A kind of fossil madrepore.
  • n. In anatomy, the serous membrane enveloping the brain and spinal cord; the middle one of the three cerebrospinal meninges, between the dura mater and the pia mater.
  • n. An old and disused name of the hyaline or hyaloid membrane within the eyeball, especially of that portion of it which contributes to form the capsule of the crystalline lens.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. air-breathing arthropods characterized by simple eyes and four pairs of legs
  • n. the middle of the 3 meninges
  • adj. relating to or resembling a member of the class Arachnida

Etymologies

New Latin arachnoīdēs, from Greek arakhnoeidēs, cobweblike : arakhnē, spider + -oeidēs, -oid.
(American Heritage® Dictionary of the English Language, Fourth Edition)
Ancient Greek ἀράχνη ("spider") + -oid (Wiktionary)

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