Naut. a device for taking bearings, consisting of a flat metal ring, equipped with sighting vanes or a small telescope, that fits over a compass card or gyrocompass
Origin:
? after L Pelorus, pilot of Hannibal's ship
See pelorus in American Heritage Dictionary 4
nounpl.pe·lo·rus·es
A fixed compass card on which bearings relative to a ship's heading are taken.