frond vs pinna

frond

noun
  • The leaf of a fern, especially a compound leaf. 

  • Any fern-like leaf or other object resembling a fern leaf. 

pinna

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

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

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

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