diadem (n.)

c. 1300, diademe, "aureole of a martyr or confessor;" mid-14c., "a crown, anything worn on the head as a mark of royalty," from Old French diademe and directly from Latin diadema "cloth band worn around the head as a sign of royalty," from Greek diadema "the headband worn by Persian kings and adopted by Alexander the Great and his successors," from diadein "to bind across," from dia "across" or "through" (see dia-) + dein "to bind," which is related to desmos "band," from PIE root *dē- "to bind." Related: Diademed.