ebony vs horse chestnut

ebony

noun
  • A tree that yields such wood. 

  • A black key on a piano or other keyboard instrument. 

  • A deep, dark black colour. 

  • A hard, dense, deep black wood from various subtropical and tropical trees, especially of the genus Diospyros. 

adj
  • Made of ebony wood. 

  • Dark-skinned; black; especially in reference to African-Americans. 

  • A deep, dark black colour. 

horse chestnut

noun
  • The large nutlike seed of these trees. 

  • Any of several tree species of genus Aesculus, especially Aesculus hippocastanum, common in temperate northern hemisphere. 

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