in antiquity, a head-band or fillet, worn by kings as a badge of their royalty. It was made of silk, thread, or wool, and tied round the temples and forehead, the ends being tied behind, and let fall on the neck. It was usually white and quite plain; though sometimes embroidered with gold, and set with pearls and precious stones. In latter times, it came to be twisted round crowns, laurels, &c. and even appears to have been worn on divers parts of the body. See Crowns. The word comes from the Latin diademum; of the Greek διάδημα, "a little band encompassing the head," of the verb διάδειν, cingo, "I gird."

in Heraldry, is applied to certain circles or rims serving to inclose the crowns of sovereign princes, and to bear the globe and cross, or the fleur de lis, for their crest. The crowns of sovereigns are bound, some with a greater and some with a less number of diadems.—The bandage about the heads of Moors on shields is also called diadem in blazoning.