palanquin vs sedan chair

palanquin

noun
  • A covered type of litter for a stretched-out passenger, carried on four poles on the shoulders of four or more bearers, as formerly used (also by colonials) in eastern Asia. 

sedan chair

noun
  • A small litter or palanquin, seating a single person, often borne on two poles and carried by two people. 

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