fossil fuel vs fuel

fossil fuel

noun
  • Any fuel derived from hydrocarbon deposits such as coal, petroleum, natural gas and, to some extent, peat; these fuels are non-renewable, and their burning moves carbon from underground into the atmosphere via the greenhouse gas carbon dioxide. 

fuel

noun
  • Substance consumed to provide energy through combustion, or through chemical or nuclear reaction. 

  • Substance that provides nourishment for a living organism; food. 

  • Something that stimulates, encourages or maintains an action. 

verb
  • To exacerbate, to cause to grow or become greater. 

  • To provide with fuel. 

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