Merriam-Webster Collegiate Dictionary - phylactery

 noun  (plural -teries)  Etymology: Middle English philaterie, from Medieval Latin philaterium, alteration of Late Latin phylacterium, from Greek phylakterion amulet, ~, from phylassein to guard, from phylak-, phylax guard  Date: 14th century  1. either of two small square leather boxes containing slips inscribed with scriptural passages and traditionally worn on the left arm and on the head by observant Jewish men and especially adherents of Orthodox Judaism during morning weekday prayers  2. amulet