penfish vs plumule

penfish

noun
  • A squid. 

  • Any of various porgies of the genus Calamus 

plumule

noun
  • A down feather. 

  • 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. 

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