• synonyms


  1. resembling a spider's web.
  2. of or belonging to the arachnids.
  3. Anatomy. of or relating to the arachnoid membrane.
  4. Botany. formed of or covered with long, delicate hairs or fibers.
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  1. an arachnid.
  2. Anatomy. the serous membrane forming the middle of the three coverings of the brain and spinal cord.
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Origin of arachnoid

1745–55; < New Latin arachnoīdes < Greek arachnoeidḗs cobweblike. See arachnid, -oid
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for arachnoid

Historical Examples

  • Cobwebby, same as arachnoid; bearing hairs like cobwebs or gossamer.

    The Elements of Botany

    Asa Gray

  • The arachnoid is a thin membrane which lies beneath the dura mater.

    A Practical Physiology

    Albert F. Blaisdell

  • All the ventricles of the brain were dilated with serum, and there was a good deal of effusion into the arachnoid and pia mater.

  • In Cortinarius, the veil is composed of arachnoid threads, and the spores are rusty.

    Fungi: Their Nature and Uses

    Mordecai Cubitt Cooke

  • When traced through the dura mater they are found to spring from the arachnoid.

British Dictionary definitions for arachnoid


  1. the middle of the three membranes that cover the brain and spinal cordSee meninges
  2. another name for arachnid
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  1. of or relating to the middle of the three meninges
  2. botany consisting of or covered with soft fine hairs or fibres
  3. of or relating to the arachnids
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for arachnoid


"cobweb-like," especially of the membrane around the brain and spinal cord, 1789, from Modern Latin arachnoides, from Greek arakhnoeides "cobweb-like," from arakhne "cobweb" (see arachnid) + -oeides (see -oid).

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Online Etymology Dictionary, © 2010 Douglas Harper

arachnoid in Medicine


  1. Resembling a cobweb. Used of the arachnoid membrane covering the brain and spinal cord.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

arachnoid in Science


  1. The delicate membrane that encloses the spinal cord and brain and lies between the pia mater and dura mater.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.