noun.
Any of various arthropods of the class Arachnida, such as spiders, scorpions, mites, and ticks, characterized by four pairs of segmented legs and a body that is divided into two regions, the cephalothorax and the abdomen.
The Century Dictionary and Cyclopedia
noun.
One of the Arachnida; an arachnidan.
the GNU version of the Collaborative International Dictionary of English