cilium vs down feather

cilium

noun
  • One of the fine hairs along an insect's wing. 

  • An eyelash. 

  • A short microscopic hairlike organelle projecting from a eukaryotic cell (such as a unicellular organism or one cell of a multicelled organism) which serve either for propulsion by causing currents in the surrounding fluid or as sensors. 

  • Hairs or similar protrusions along the margin of an organ. 

down feather

noun
  • A feather of the down of a bird 

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