assart vs headroom

assart

verb
  • To clear forest land for agriculture; remove stumps. 

noun
  • Forest land cleared for agriculture. 

headroom

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

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

  • 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 assart and headroom occurred in a corpus of books? (source: Google Ngram Viewer )