arachnoid

American  

[uh-rak-noid] / əˈræk nɔɪd /

adjective

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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noun

1. an arachnid.

2. Anatomy. the serous membrane forming the middle of the three coverings of the brain and spinal cord.

arachnoid British  

/ əˈræknɔɪd /

noun

1. the middle of the three membranes that cover the brain and spinal cord See meninges

2. another name for arachnid

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adjective

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

arachnoid Scientific  

/ ə-răk′noid′ /

1. The delicate membrane that encloses the spinal cord and brain and lies between the pia mater and dura mater.

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Etymology

Origin of arachnoid

1745–55; < New Latin arachnoīdes < Greek arachnoeidḗs cobweblike. See arachnid, -oid

Example Sentences

Ortiz, 42, plays Rocky, an arachnoid alien made of stone-like material, who befriends Grace.

From Los Angeles Times • Apr. 7, 2026

Lopez plays dual roles as a movie actor and an arachnoid goddess and she sauntered into the Sundance premiere channeling the power of both.

From Los Angeles Times • Feb. 2, 2025

Large veins are known to pass through the arachnoid barrier carrying blood away from the brain, and these were clearly observed on the MRI scans.

From Science Daily • Feb. 7, 2024

The meninges comprise three layers that surround the brain: pia, arachnoid and dura.

From Salon • Nov. 20, 2022

On post-mortem examination there was not the slightest appearance of any meningeal lesion, except a few dark spots like sanguineous effusion under the arachnoid.

From A System of Practical Medicine by American Authors, Vol. I Volume 1: Pathology and General Diseases by Various