oilskin vs tegument

oilskin

noun
  • A raincoat made from cotton fabric treated with oil and pigment to make it waterproof. 

  • Cloth made from cotton and treated with oil and pigment to make it waterproof. 

  • Foul-weather gear worn by sailors, whether of natural or synthetic materials. 

tegument

noun
  • Something which covers; a covering or coating. 

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