hostler vs ostler

hostler

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

  • A person employed to care for a locomotive or other large engine. 

ostler

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

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