any wingless, carnivorous arthropod of the class Arachnida, including spiders, scorpions, mites, ticks, and daddy-longlegs, having a body divided into two parts, the cephalothorax and the abdomen, and having eight appendages and no antennae.Compare insect.


belonging or pertaining to the arachnids.

Origin of arachnid

1865–70; < New Latin Arachnida < Greek aráchn(ē) spider, spider's web + New Latin -ida -ida
Related formsa·rach·ni·dan [uh-rak-ni-duh n] /əˈræk nɪ dən/, adjective, noun Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Related Words for arachnid

tick, mite, tarantula, scorpion, harvestman

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Contemporary Examples of arachnid

Historical Examples of arachnid

British Dictionary definitions for arachnid



any terrestrial chelicerate arthropod of the class Arachnida, characterized by simple eyes and four pairs of legs. The group includes the spiders, scorpions, ticks, mites, and harvestmen
Derived Formsarachnidan, adjective, noun

Word Origin for arachnid

C19: from New Latin Arachnida, from Greek arakhnē spider
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 arachnid

"a spider," 1869, from French arachnide (1806) or Modern Latin Arachnida, introduced as name for this class of arthropods 1815 by French biologist Jean Baptiste Pierre Antoine de Monet de Lamarck (1744-1829), from Greek arakhne (fem.) "spider; spider's web," which probably is cognate with Latin aranea "spider, spider's web" (borrowed in Old English as renge "spider"), from aracsna. The Latin word could be a Greek borrowing or both could be from a common root. An earlier noun form was arachnidian (1828).

Online Etymology Dictionary, © 2010 Douglas Harper

arachnid in Science



Any of various arthropods of the class Arachnida, such as spiders, scorpions, mites, and ticks. Arthropods are characterized by four pairs of segmented legs and a body that is divided into two regions, the cephalothorax and the abdomen.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.