equerry vs ostler

equerry

noun
  • An officer responsible for the care and supervision of the horses of a person of rank. 

  • A personal attendant to a head of state, a member of a royal family, or a national representative. 

ostler

noun
  • A person employed at an inn, hostelry, or stable to look after horses; a groom 

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