glade vs polar cap

glade

noun
  • A bright surface of ice or snow. 

  • An everglade. 

  • An open passage through a wood; a grassy open or cleared space in a forest. 

  • An open space in the ice on a river or lake. 

polar cap

noun
  • A high-latitude region of a celestial body that is covered by ice. 

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