fluid vs natural gas

fluid

noun
  • A liquid (as opposed to a solid or gas). 

  • Any substance which can flow with relative ease, tends to assume the shape of its container, and obeys Bernoulli's principle; a liquid, gas or plasma. 

  • Intravenous fluids. 

adj
  • In a state of flux; subject to change. 

  • Of or relating to fluid. 

  • Moving smoothly, or giving the impression of a liquid in motion. 

  • Convertible into cash. 

  • Genderfluid. 

natural gas

noun
  • A mixture of gaseous hydrocarbons associated with petroleum deposits; mostly methane with smaller amounts of ethane, propane and butane; principally used as a fuel. 

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