Easton's Bible Dictionary

Diadem - the tiara of a king (Ezek. 21:26; Isa. 28:5; 62:3); the turban (Job 29:14). In the New Testament a careful distinction is drawn between the diadem as a badge of royalty (Rev. 12:3; 13:1; 19:12) and the crown as a mark of distinction in private life. It is not known what the ancient Jewish "diadem" was. It was the mark of Oriental sovereigns. (See CROWN.)