glade vs glen

glade

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

  • An everglade. 

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

  • A bright surface of ice or snow. 

glen

noun
  • A secluded and narrow valley, especially one with a river running through it; a dale; a depression between hills. 

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