1. Judaism. either of two small, black, leather cubes containing a piece of parchment inscribed with verses 4–9 of Deut. 6, 13–21 of Deut. 11, and 1–16 of Ex. 13: one is attached with straps to the left arm and the other to the forehead during weekday morning prayers by Orthodox and Conservative Jewish men.
2. (in the early Christian church) a receptacle containing a holy relic.
3. an amulet, charm, or safeguard against harm or danger.
"Billy, put down that phylactery; we are Episcopalian."
Sorry, the sentence isn't mine. I saw The 25th Annual Putnam County Spelling Bee this weekend.