lanugo vs thatch

lanugo

noun
  • Soft down or fine hair, specifically that covering the human foetus or a tumorous area. 

thatch

noun
  • Any straw-like material, such as a person's hair. 

  • Straw, rushes, or similar, used for making or covering the roofs of buildings, or of stacks of hay or grain. 

  • A buildup of cut grass, stolons or other material on the soil in a lawn. 

  • Any of several kinds of palm, the leaves of which are used for thatching. 

verb
  • To cover the roof with straw, reed, leaves, etc. 

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