1911 Encyclopædia Britannica/Perpent

PERPENT, or Parpent Stones, in architecture, bond or “through stones,” the διατόνοι of the Greeks and Romans, long stones going right through walls, and tying them together from face to face. The O. Fr. parpain, modern parpaing, from which this word is derived, is obscure in origin. It may be from a supposed Lat. perpago, perpaginis, formed like compago, a joint, from the root of pangere, to fasten, and meaning “something fastened together,” or from some popular corruption of Lat. perpendiculum, plummet or plumb-line (pir or pendere, to hang), referring to the smooth perpendicular faces of the stone.