headrest vs prie-dieu

headrest

noun
  • The part of a seat designed to support the sitter's head. 

prie-dieu

noun
  • A piece of furniture on which someone can pray, consisting of a cushioned area to kneel on, with a built-in ledge for books. 

How often have the words headrest and prie-dieu occurred in a corpus of books? (source: Google Ngram Viewer )