phylaktērion

Phylaktḗrion is Greek for a safeguard, a protective charm, from phylássein (to guard, to protect). In the New Testament (Matthew 23:5), Jesus criticizes the Pharisees for making their phylacteries wide — referring to the tefillin, small leather boxes containing Torah passages that observant Jews bind to the arm and forehead during morning prayer. The Greek word was applied to a Jewish religious object that was not an amulet — the tefillin are not charms but reminders of divine commandments.

The confusion between phylactery (protective amulet) and tefillin (ritual prayer object) has persisted for two millennia. Jews use the Hebrew word tefillin. Christians used the Greek phylacterion. The New Testament application conflated a religious practice with superstition. The word entered English with this loaded history — it meant Jewish prayer boxes, but the Greek etymology implied magic.

In the twentieth century, Dungeons & Dragons borrowed 'phylactery' for a completely new use. In D&D lore, a lich (an undead wizard) stores its soul in a phylactery — an object that must be destroyed to kill the lich permanently. This usage, invented by game designers, draws on the Greek meaning (a protective container) rather than the Jewish practice. It has no connection to tefillin, but the word's association with dark magic in D&D has become its most recognized meaning among younger English speakers.

The word now has three meanings: a Greek amulet, a Jewish prayer object, and a fantasy villain's soul container. The first is historical, the second is religious, the third is fictional. None of the three groups that use the word means the same thing by it.