Definition of "arachnoid" []

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The inflammation results in thickening of the middle membrane, called the arachnoid, causing it to adhere to structures near it."
• "In the arachnoid membrane are small areas called arachnoid villi (vil'eye; "tufts of hair" L, so named because they have the appearance of tiny tufts)."
• "Finally, within the spaces of the arachnoid is a lymph-like liquid which completely envelops the brain and the cord, and which, by serving as a watery cushion, protects them from jars and shocks."