The tiara of a king (Ezek. 21:26; Isaiah 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 (Revelation 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.)

Noah Webster's New International Dictionary of the English Language

1. (n.) Originally, an ornamental head band or fillet, worn by Eastern monarchs as a badge of royalty; hence (later), also, a crown, in general.

2. (n.) Regal power; sovereignty; empire; -- considered as symbolized by the crown.

3. (n.) An arch rising from the rim of a crown (rarely also of a coronet), and uniting with others over its center.

4. (v. t.) To adorn with a diadem; to crown.