diadem vs headdress

diadem

noun
  • An ornamental headband worn as a badge of royalty. 

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

  • A crown. 

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

verb
  • To adorn with a diadem; to crown. 

headdress

noun
  • A decorative covering or ornament worn on the head. 

  • A hairdo. 

How often have the words diadem and headdress occurred in a corpus of books? (source: Google Ngram Viewer )