booster cushion vs hassock

booster cushion

hassock

noun
  • A cushion used primarily in churches for kneeling on while praying. 

  • A thick cushion used as a seat; an ottoman or pouffe. 

  • A dense clump of grass or vegetation; a tussock. 

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