diadem

Short definition from Wiktionary

Noun

1. 1
   An ornamental headband worn as a badge of royalty.
2. 2
   A crown.
3. 3
   Regal power; sovereignty; empire—considered as symbolized by the crown.
4. 4
   An arch rising from the rim of a crown (rarely also of a coronet), and uniting with others over its centre.

Verb

1. 1
   To adorn with a diadem; to crown.