coating vs cortex

coating

noun
  • A thin outer layer. 

  • A telling-off; a reprimand. 

cortex

noun
  • The outer layer of an internal organ or body structure, such as the kidney or the brain. 

  • The tissue of a stem or root that lies inward from the epidermis, but exterior to the vascular tissue. 

  • The outer surface of a piece of flint. 

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