bowstring vs gradation

bowstring

noun
  • The string of an archer's bow. 

  • The string of an archer's bow, as used by the Turks for strangling offenders. 

verb
  • To strangle with a bowstring. 

gradation

noun
  • A diatonic succession of chords. 

  • A calibration marking. 

  • A passing by small degrees from one tone or shade, as of color, to another. 

  • Apophony. 

  • A gradual change within one parameter, or an overlapping of two blocks of sound. 

  • A sequence of gradual, successive stages; a systematic progression. 

  • Any degree or relative position in an order or series. 

  • The act of gradating or arranging in grades. 

verb
  • To form with gradations. 

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