tomentum vs vellus hair

tomentum

noun
  • A covering of fine, soft hairs; a pubescence. 

  • A mass of filamentous hairs on the leaf of a plant. 

  • A network of fine blood vessels between the pia mater and the cerebral cortex. 

vellus hair

noun
  • An individual strand of vellus hair 

  • Short, fine, light-colored, and barely noticeable hair that develops on most of a person's body from his/her childhood. 

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