abra vs clough

abra

noun
  • a narrow mountain or mesa pass 

  • a wooden boat used as a ferry in Dubai 

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. 

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