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late 14c., "small leathern box containing four Old Testament texts," from Old French filatiere (12c.) and directly from Medieval Latin philaterium, from Late Latin phylacterium "reliquary," from Greek phylacterion "safeguard, amulet," noun use of neuter of adjective phylakterios "serving as a protection," from phylakter "watcher, guard," from phylassein "to guard or ward off," from phylax (genitive phylakos) "guard," of unknown origin. Sometimes worn on the forehead, based on a literal reading of scripture:
Ye shall bind them [my words] for a sign upon your hands, and they shall be for frontlets between your eyes. [Deut. xi:18]
in Jewish religious practice, one of two small, black leather, cube-shaped cases containing Torah texts written on parchment, which, in accordance with Deuteronomy 6:8 (and similar statements in Deuteronomy 11:18 and Exodus 13:9, 16), are to be worn by male Jews of 13 years and older as reminders of God and of the obligation to keep the Law during daily life. The name phylactery is derived from the Greek phylakterion, meaning amulet.