arachnid

noun

arach·​nid ə-ˈrak-nəd 

-ˌnid

: any of a class (Arachnida) of arthropods comprising chiefly terrestrial invertebrates, including the spiders, scorpions, mites, and ticks, and having a segmented body divided into two regions of which the anterior bears four pairs of legs but no antennae

arachnid adjective

Did you know?

The term arachnid refers to a class of animals that includes spiders, scorpions, mites, and ticks. Most arachnids have a segmented body divided into two regions, with the front part bearing four pairs of legs, but no antennae. They have a hard external skeleton and range in size from the mite, which is 0.003-in (0.08-mm) long, to the 8-in (21-cm) black scorpion of Africa. As arachnids grow, they molt, or shed their skin, several times. Arachnids are primarily carnivorous, but most are unable to digest food internally, instead they inject their prey with digestive fluids, then suck the liquefied remains. Arachnids are found worldwide in nearly every habitat. Some mites and ticks are parasitic and can carry diseases. Venomous spiders and scorpions also may pose a danger to humans, but most arachnids are harmless and prey only on insects.

Examples of arachnid in a Sentence

Spiders, scorpions, mites, and ticks are arachnids.

Recent Examples on the Web

This threat applies to at least a quarter of the species in six different classes, including arachnids and chilopodans (centipedes), as well as anthozoans and hydrozoans (marine invertebrates related to jellyfish and corals), according to the study, published on Tuesday in BioScience. —Sharon Udasin, The Hill, 20 May 2025

This resin captured a remarkable diversity of organisms — from insects and arachnids to frogs, snakes and even fragments of dinosaurs — offering an unparalleled window into ancient tropical forest ecosystems. —Scott Travers, Forbes.com, 29 Apr. 2025

The stars of the exhibit are live tarantulas representing over a dozen species, as well as other arachnids including the vinegaroon, hairy desert scorpion, Asian giant centipede, peppered cockroach, Madagascar hissing roach and darkling beetle. —Emily McClanathan, Chicago Tribune, 11 Feb. 2025

Scorpions are not typically found in the Boston area but over 2,000 species of the predatory arachnids exist worldwide, according to the Mayo Clinic. —Jon Haworth, ABC News, 4 Mar. 2025

Word History

First Known Use

1826, in the meaning defined above

Kids Definition

arachnid

noun

arach·​nid ə-ˈrak-nəd 

-ˌnid

: any of a class of arthropods including the spiders, scorpions, mites, and ticks and having a segmented body divided into two regions of which the front part bears four pairs of legs but no antennae

arachnid adjective