What is the meaning of Diadem?

An ornamental headband worn as a badge of royalty.

A crown.

Regal power; sovereignty; empire—considered as symbolized by the crown.

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

To adorn with a diadem; to crown.

diadem, tiara

diadem (ornamental headband)

Alternative form of diademă

diadem, tiara

Source: wiktionary.org