Definition of diadem

• n. - Originally, an ornamental head band or fillet, worn by Eastern monarchs as a badge of royalty; hence (later), also, a crown, in general.
• n. - Regal power; sovereignty; empire; -- considered as symbolized by the crown.
• n. - An arch rising from the rim of a crown (rarely also of a coronet), and uniting with others over its center.
• v. t. - To adorn with a diadem; to crown.