booster cushion vs kneeler

booster cushion

kneeler

noun
  • A person who kneels. 

  • On a gable-end, the stone (often decorated) at the base of the slope of the gable on either side. 

  • A hassock. 

  • An apparatus that permits the loading door of a bus to decrease in height in order to facilitate boarding of passengers that are seniors and physically disadvantaged 

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