clough vs couloir

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. 

couloir

noun
  • A steep gorge along a mountainside. 

  • A corridor or passage. 

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