heavy metal vs singing

heavy metal

noun
  • A genre descended from rock music, characterized by massive sound, highly amplified distortion, and overall loudness, often with extended guitar solos, and lyrics that involve aggressive or fantastic imagery. 

  • Any metal that has a specific gravity greater than about 5, especially one, such as lead, that is poisonous and may be a hazard in the environment. (There are many different definitions of what counts as a heavy metal; see Heavy metals for a discussion.) 

  • Great influence or power. 

  • guns or shot of large size. 

singing

noun
  • The act of using the voice to produce musical sounds; vocalizing. 

  • A gathering for the purpose of singing shape note songs. 

  • Disclosing information, or giving evidence about another. 

adj
  • Producing a whistling sound due to the escape of steam. 

  • Smooth and flowing. 

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