Penta- (from the Greek word for "five") turns up in plenty of English terms. They range from the magical or talismanic star symbol called a pentangle, to the literary pentalogy (a series of five closely related published works), to the ancient five-stringed musical instrument called a pentachord, to the athletic pentathlon that has been part of both the ancient and the modern Olympic games. And we turned up scores—or should we say pentadecs (groups of fifteen)—of scientific penta- terms, everything from pentode (a vacuum tube with five electrodes) to pentryl (a five-part explosive) to pentastomum, a genus of five-stomached tongue worms that are chiefly parasitic in carnivorous animals.