Word Origin & History
c.1380, "small leathern box containing four O.T. texts," from O.Fr. filatiere (12c.), from L.L. phylacterium "reliquary," from Gk. phylacterion "safeguard, amulet," properly neut. of adj. phylakterios "serving as a protection," from phylakter "watcher, guard," from phylassein "to guard or ward off,"
from phylax (gen. 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]