kola vs kola nut

kola

noun
  • A tree, genus Cola, bearing large brown seeds ("nuts") that are the source of cola extract. 

  • A nut of this tree. 

kola nut

noun
  • The edible seed of the kola tree, Cola acuminata and related species, used as a flavoring and as a source of caffeine. 

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