clough vs ravine

clough

noun
  • A narrow valley; a cleft in a hillside; a ravine, glen, or gorge. 

  • A sluice used in returning water to a channel after depositing its sediment on the flooded land. 

  • The cleft or fork of a tree; crotch. 

  • A wood; weald. 

ravine

noun
  • A deep narrow valley or gorge in the earth's surface worn by running water. 

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