hairline vs thinning

hairline

adj
  • very thin, as thin as a hair 

noun
  • A fishing line made from hair. 

  • The line along one's forehead where hair starts growing. 

  • A very thin line in writing, drawing, or typography. 

  • A very thin fissure. 

thinning

adj
  • Becoming less thick, dense, or numerous 

noun
  • Wood, leaves, or other plant parts removed during the process of thinning 

  • The action or result of reducing thickness, density, or number 

  • Process of removing plants or parts of plants to facilitate the growth of other plants 

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