diadem

/ˈdaɪəˌdɛm/
noun
  1. A small crown or jeweled headband worn as a symbol of royalty or honor.
    • The queen placed a golden diadem on her head for the coronation.
    • In the museum, we saw an ancient diadem studded with emeralds.
    • She wore a simple diadem of silver leaves to the formal ball.
  2. Something that crowns or adorns like a crown; a crowning achievement or feature.
    • The garden's diadem was a fountain surrounded by roses.
    • The mountain peak was a diadem of snow against the blue sky.
    • Her latest novel is the diadem of her literary career.