frith vs undergrowth

frith

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

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

  • A forest or wood; woodland generally. 

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

undergrowth

noun
  • The plants in a forest which only reach a relatively low height (such as shrubs and bushes). 

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