mesa vs tor

mesa

noun
  • Flat area of land or plateau higher than other land, with one or more clifflike edges. 

tor

noun
  • A hill with such rock formation. 

  • A craggy outcrop of rock on the summit of a hill, created by the erosion and weathering of rock. 

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