arachn(o)-

A spider or spiders.

Greek arakhnē, spider.

Somebody frightened of spiders is said to have arachnophobia; the study of spiders—and the other Arachnida, a class of arthropods that also includes scorpions, mites, and ticks—is arachnology; an arachnid is a member of this group; the associated adjective is arachnoid.