monotonous vs sing-song

monotonous

adj
  • Having an unvarying pitch or tone. 

  • Tedious, repetitious, or lacking in variety. 

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. 

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