arachnoid

adjective (1)
arach·​noid | \ə-ˈrak-ˌnȯid \

Definition of arachnoid 

(Entry 1 of 3)

1 : of or relating to a thin membrane of the brain and spinal cord that lies between the dura mater and the pia mater

2 : covered with or composed of soft loose hairs or fibers

arachnoid

noun

Definition of arachnoid (Entry 2 of 3)

: an arachnoid membrane

arachnoid

adjective (2)

Definition of arachnoid (Entry 3 of 3)

: resembling or related to the arachnids

First Known Use of arachnoid

Adjective (1)

1789, in the meaning defined at sense 1

Noun

1804, in the meaning defined above

Adjective (2)

1825, in the meaning defined above

History and Etymology for arachnoid

Noun

New Latin arachnoides, from Greek arachnoeidēs, like a cobweb, from arachnē spiderweb

Adjective (2)

New Latin Arachnida + English -oid

Keep scrolling for more

Learn More about arachnoid

Statistics for arachnoid

Look-up Popularity

Time Traveler for arachnoid

The first known use of arachnoid was in 1789

See more words from the same year

Keep scrolling for more

More Definitions for arachnoid

arachnoid

noun
arach·​noid | \ə-ˈrak-ˌnȯid \

Medical Definition of arachnoid 

(Entry 1 of 2)

: a thin membrane of the brain and spinal cord that lies between the dura mater and the pia mater

arachnoid

adjective
variants: also arachnoidal \ ə-​ˌrak-​ˈnȯid-​ᵊl \

Medical Definition of arachnoid (Entry 2 of 2)

: of or relating to the arachnoid the arachnoid membrane

More from Merriam-Webster on arachnoid

See words that rhyme with arachnoid

Comments on arachnoid

What made you want to look up arachnoid? Please tell us where you read or heard it (including the quote, if possible).

WORD OF THE DAY

noxious or harmful

Get Word of the Day daily email!

Test Your Vocabulary

A Thanksgiving Word Quiz

  • a-traditional-thanksgiving-dinner
  • November comes from a word for which of the following numbers?
Name That Thing

Test your visual vocabulary with our 10-question challenge!

TAKE THE QUIZ
Dictionary Devil

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!