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

Ticks cause disease, including a meat allergy Ticks are small, eight-legged bloodsucking parasites — arachnids, not insects — that feed on animals and sometimes people. —Mike Stobbe, Chicago Tribune, 25 Apr. 2026

Ticks are small, eight-legged bloodsucking parasites — arachnids, not insects — that feed on animals and sometimes people. —ABC News, 25 Apr. 2026

Dust mites are microscopic arachnids related to ticks, spiders, and chiggers. —Karen Brewer Grossman, Southern Living, 25 Apr. 2026

Since its arrival – likely as a hitchhiker on a shipping container or an airplane from Asia, experts say – the arachnid has been steadily marching north. —Khloe Quill, FOXNews.com, 27 Mar. 2026

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