pentacle (n.)

1590s, "mathematical figure (presumably originally one of five points) used in magical ceremonies and considered a defense against demons," from Medieval Latin pentaculum "pentagram," a hybrid coined from Greek pente "five" (from PIE root *penkwe- "five") + Latin -culum, diminutive (or instrumental) suffix. OED notes other similar words: Italian had pentacolo "anything with five points," and French pentacle (16c.) was the name of something used in necromancy, perhaps a five-branched candlestick; French had pentacol "amulet worn around the neck" (14c.), from pend- "to hang" + a "to" + col "neck." The same figure as a pentagram, except in magical usage, where it has been extended to other symbols of power, including a six-point star. Related: Pentacular.