hassock vs tussock

hassock

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

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

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

tussock

noun
  • A tuft or clump of green grass or similar verdure, forming a small hillock. 

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