Di·a·dem n.
 1. Originally, an ornamental head band or fillet, worn by Eastern monarchs as a badge of royalty; hence (later), also, a crown, in general. “The regal diadem.”
 2. Regal power; sovereignty; empire; -- considered as symbolized by the crown.
 3. Her. An arch rising from the rim of a crown (rarely also of a coronet), and uniting with others over its center.
 Diadem lemur. Zool. See Indri.
 Diadem spider Zool., the garden spider.