a very poisonous, medium-sized spider (Loxosceles reclusa), common in the U.S., having a violin-shaped mark on its cephalothorax and only six eyes
See brown recluse spider in American Heritage Dictionary 4
noun
A venomous spider (Loxosceles reclusa) having an hourglass-shaped mark on the cephalothorax, introduced into the southern United States from South America.