tuffet vs tussock

tuffet

noun
  • A clump of grass or similar vegetation; a small grass-covered mound. 

  • An inflatable cushion serving as landing area for precision accuracy parachuting. 

  • A large cushion which may have an internal frame, used as a low seat or stool. 

tussock

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

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