feathers vs plumule

feathers

plumule

noun
  • One of the featherlike scales of certain male butterflies. 

  • The aftershaft of a feather. 

  • The first bud, or growing point, of a plant embryo, situated above the cotyledons. 

  • A down feather. 

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