autonomous vs voluntary

autonomous

adj
  • Acting on one's own or independently; of a child, acting without being governed by parental or guardian rules. 

  • Self-governing. Intelligent, sentient, self-aware, thinking, feeling, governing independently. 

  • Used with no subject, indicating an unknown or unspecified agent; used in similar situations as the passive in English (the difference being that the theme in the English passive construction is the subject, while in the Celtic autonomous construction the theme is the object and there is no subject). 

voluntary

adj
  • Done, given, or acting of one's own free will. 

  • Done by design or intention; intentional. 

  • Of or relating to voluntarism. 

  • Endowed with the power of willing. 

  • Working or done without payment. 

noun
  • A supporter of voluntarism; a voluntarist. 

  • A short piece of music, often having improvisation, played on a solo instrument. 

  • A volunteer. 

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