frith vs underbrush

frith

noun
  • A forest or wood; woodland generally. 

  • Brushwood or undergrowth, sometimes in the form of a hedge. 

  • Land with mostly undergrowth and few trees; also, land in between forests or woods; pastureland which is not in use. 

  • A hedge, especially one made from brushwood which has been wattled; also, a movable frame made from wattled branches, a hurdle. 

underbrush

noun
  • The small trees and other plants that clutter the floor of a forest. 

verb
  • To clear (an area) of underbrush. 

  • To work among the underbrush. 

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