- air-breathing arthropods described as quick eyes and four pairs of feet
- An arachnidan.
"a spider," 1869, from French arachnide (1806) or contemporary Latin Arachnida, launched as title because of 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 most likely is cognate with Latin aranea "spider, spider's web" (lent in Old English as renge "spider"), from aracsna. The Latin word could be a Greek borrowing from the bank or both could possibly be from a typical root. An earlier noun form had been arachnidian (1828).
a small grouping of insects recognized for having four pairs of feet and either one or two actual sections; spiders are the most well-known of all arachnids.
(letter.) An arachnidan.
In several families of spiders, but principally in those like the Clubionidae and Salticidae, which are terrestrial in habits, there are species which not only live amongst ants, but so closely resemble them in their shape, size, colour and actions that it requires a practised eye to distinguish the Arachnid from the insect.