hairline vs sparse

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. 

sparse

adj
  • Not dense; meager; scanty 

  • Having few nonzero elements 

  • Having widely spaced intervals. 

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