sing-song vs toneless

sing-song

adj
  • Like a piece of sing-song; simple and melodic, song-like. 

noun
  • A kind of verse with a simple, song-like rhythm. 

  • An informal gathering involving group singing. 

toneless

adj
  • Lacking tone or pitch, have the neutral tone. 

  • Lacking tone or expression. 

  • Lacking vitality; listless. 

How often have the words sing-song and toneless occurred in a corpus of books? (source: Google Ngram Viewer )