diethyl ether vs ethyl ether

diethyl ether

noun
  • A clear, colorless, highly flammable liquid with a low boiling point and chemical formula CH₃-CH₂-O-CH₂-CH₃. Used as a solvent and in the past as a general anesthetic. 

ethyl ether

noun
  • Synonym of diethyl ether 

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