What is the X in X-mas?
"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).