glade vs headroom

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. 

headroom

noun
  • The vertical clearance above someone's head, as in a tunnel, doorway etc. 

  • The ability of a system to reproduce loud sounds free of distortion; dynamic headroom. 

  • The vertical measurement, top to bottom, for example for clearance under a bridge. 

  • The distance between the actual performance of an algorithm and its maximum possible performance. 

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