motte vs tor

motte

noun
  • A raised earth mound, often topped with a wooden or stone structure and surrounded with a ditch. 

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 motte and tor occurred in a corpus of books? (source: Google Ngram Viewer )