pinna vs plumule

pinna

noun
  • A feather, wing, fin, or other similar appendage. 

  • The visible part of the ear that resides outside of the head, the auricle; outer ear excluding the ear canal. 

  • A leaflet or primary segment of a pinnate compound leaf. 

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 pinna and plumule occurred in a corpus of books? (source: Google Ngram Viewer )