oil vs oil slick

oil

noun
  • petroleum 

  • petroleum-based liquid used as fuel or lubricant. 

  • Liquid fat. 

  • An oil painting. 

  • Oil paint. 

  • Containing oil, conveying oil; intended for or capable of containing oil. 

verb
  • To lubricate with oil. 

  • To grease with oil for cooking. 

oil slick

noun
  • A thin film of oil floating on the surface of water, especially one that has leaked or been discharged from a ship etc 

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