crude vs petroleum

crude

noun
  • Crude oil. 

  • Any substance in its natural state. 

adj
  • In a natural, untreated state. 

  • Characterized by simplicity, especially something not carefully or expertly made. 

  • Lacking tact or taste. 

  • Lacking concealing elements. 

  • Pertaining to the uninflected stem of a word. 

petroleum

noun
  • A flammable liquid ranging in color from clear to very dark brown and black, consisting mainly of hydrocarbons, occurring naturally in deposits under the Earth's surface. 

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