heavy metal vs iron

heavy metal

noun
  • guns or shot of large size. 

  • 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. 

iron

noun
  • A firearm, either a long gun or a handgun. 

  • A common, inexpensive metal, silvery grey when untarnished, that rusts, is attracted by magnets, and is used in making steel. 

  • A golf club used for middle-distance shots. 

  • Any material, not a steel, predominantly made of elemental iron. 

  • A dark shade of the color silver. 

  • A tool or appliance made of metal, which is heated and then used to transfer heat to something else; most often a thick piece of metal fitted with a handle and having a flat, roughly triangular bottom, which is heated and used to press wrinkles from clothing, and now usually containing an electrical heating apparatus. 

  • shackles. 

  • A male homosexual. 

  • A metallic chemical element having atomic number 26 and symbol Fe. 

  • Used as a symbol of great strength or toughness, or to signify a very strong or tough material. 

  • A meteorite consisting primarily of metallic iron (mixed with a small amount of nickel), as opposed to one composed mainly of stony material. 

  • A safety curtain in a theatre. 

  • dumb bombs, those without guidance systems. 

  • Weight used as resistance for the purpose of strength training. 

adj
  • Made of the metal iron. 

  • Strong (as of will), inflexible. 

verb
  • To pass an iron over (clothing or some other item made of cloth) in order to remove creases. 

  • To furnish or arm with iron. 

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