flight feather vs plumule

flight feather

noun
  • Any asymmetrical feather of the wing or tail of a bird. 

plumule

noun
  • The aftershaft of a feather. 

  • One of the featherlike scales of certain male butterflies. 

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

  • A down feather. 

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