ectoderm vs wool

ectoderm

noun
  • Outermost of the three tissue layers in the embryo of a metazoan animal. Through development, it will produce the epidermis (skin) and nervous system of the adult. 

wool

noun
  • The hair of the sheep, llama and some other ruminants. 

  • Anything with a texture like that of wool. 

  • Yarn, including that made from synthetic fibers. 

  • A cloth or yarn made from the wool of sheep. 

  • A fine fiber obtained from the leaves of certain trees, such as firs and pines. 

  • A resident of a satellite town outside Liverpool, such as St Helens or Warrington. See also Yonner. 

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