Definition

1. Adjective:

   • Relating to or resembling arachnids: Pertaining to the class Arachnida, which includes spiders, scorpions, ticks, and mites, or having a similar appearance.
   • Resembling a spider's web; cobweb-like: Having a fine, delicate, web-like structure.

2. Noun:

   • A member of the class Arachnida: An air-breathing arthropod, such as a spider or scorpion, characterized by having simple eyes and four pairs of legs. (Note: This usage is less common; the typical term is "arachnid").
   • (Anatomy) The arachnoid mater: The middle of the three meninges, the membranes that envelop the brain and spinal cord. It is a delicate, web-like membrane located between the dura mater and the pia mater.

Usage Examples

• Adjective:

  • The plant's seed pods had an arachnoid covering of fine hairs. (The seed pods were covered with a delicate, web-like layer of hairs.)
  • Under the microscope, the crystal structure appeared arachnoid. (The structure of the crystals looked like a spider's web.)

• Noun (Anatomy):

  • Cerebrospinal fluid flows in the subarachnoid space, which is below the arachnoid. (The fluid circulates in the space beneath the arachnoid membrane.)
  • The surgeon carefully incised the arachnoid to access the underlying brain tissue. (The surgeon cut the delicate arachnoid membrane.)

Advanced Usage

• "Arachnoid granulations": (Anatomy) Small protrusions of the arachnoid mater into the venous sinuses of the brain, which allow cerebrospinal fluid to re-enter the bloodstream.

  • The blockage of the arachnoid granulations can lead to a condition called hydrocephalus.

• "Arachnoid cyst": (Medicine) A cerebrospinal fluid-filled sac that develops between the arachnoid membrane and the brain or spinal cord.

  • The MRI scan revealed a small, benign arachnoid cyst.

Variants and Related Words

• Arachnid (n): The more common term for a member of the class Arachnida (e.g., spider, scorpion).
• Arachnophobia (n): An extreme or irrational fear of spiders and other arachnids.
• Subarachnoid (adj): Located or occurring beneath the arachnoid membrane, especially the "subarachnoid space" containing cerebrospinal fluid.
• Arachnoidal (adj): An alternative adjective form meaning "of or relating to the arachnoid membrane."

Synonyms

• Adjective (web-like): Cobwebby, filamentous, gossamer.
• Noun (arachnid): (Use "arachnid" as the standard synonym).
• Noun (membrane): Arachnoid mater (full anatomical term).

Related Phrases

• Arachnoid mater: The full Latin-derived name for the anatomical membrane.
• Arachnoid villi: Another term for arachnoid granulations.

Adjective

1. relating to or resembling a member of the class Arachnida

Noun

1. air-breathing arthropods characterized by simple eyes and four pairs of legs
2. the middle of the 3 meninges