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]
(Gr. phulakteria; i.e., "defences" or "protections"), called by modern Jews tephillin (i.e., "prayers") are mentioned only in Matt. 23:5. They consisted of strips of parchment on which were inscribed these four texts: (1.) Ex. 13:1-10; (2.) 11-16; (3.) Deut. 6:4-9; (4.) 11:18-21, and which were enclosed in a square leather case, on one side of which was inscribed the Hebrew letter shin, to which the rabbis attached some significance. This case was fastened by certain straps to the forehead just between the eyes. The "making broad the phylacteries" refers to the enlarging of the case so as to make it conspicuous. (See FRONTLETS.) Another form of the phylactery consisted of two rolls of parchment, on which the same texts were written, enclosed in a case of black calfskin. This was worn on the left arm near the elbow, to which it was bound by a thong. It was called the "Tephillah on the arm."