cilium vs rectrix

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. 

rectrix

noun
  • A flight feather on the tails of birds, used for directional control. 

  • A governess; a rectoress. 

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