heavy metal vs instrumental

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. 

instrumental

noun
  • A composition written or performed without lyrics, sometimes using a lead instrument to replace vocals. 

  • The instrumental case. 

adj
  • Pertaining to, made by, or prepared for an instrument, especially a musical instrument (rather than the human voice). 

  • Applied to a case expressing means or agency, generally indicated in English by by or with with the objective. 

  • Serving as an instrument, medium, means, or agency. 

  • essential or central; of great importance or relevance. 

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