overtone vs self-suggestion

overtone

noun
  • An implicit message (in a film, book, verbal discussion or similar) perceived as overwhelming the explicit message. 

  • A tone whose frequency is an integer multiple of another; a member of the harmonic series. 

verb
  • To give an overtone to. 

self-suggestion

noun
  • Synonym of autosuggestion 

How often have the words overtone and self-suggestion occurred in a corpus of books? (source: Google Ngram Viewer )