queen mother vs sultana

queen mother

noun
  • A widowed queen consort (a queen dowager) whose son or daughter from that marriage is the reigning monarch. 

sultana

noun
  • A wife or mistress of a sultan. 

  • A female ruler of a sultanate. 

  • An old form of necklace. 

  • A pale yellow raisin made from a seedless grape. 

  • A type of viol, a cither viol. 

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