cast iron vs fierce

cast iron

adj
  • Durable; tough; resilient. 

  • Inflexible or without exception. 

  • Made of cast iron. 

noun
  • A hard and brittle, but strong, alloy of iron, carbon, and silicon, formed by casting in a mould. 

fierce

adj
  • Resolute or strenuously active. 

  • Excellent, very good. 

  • Exceedingly violent, severe, ferocious, cruel or savage. 

  • Of exceptional quality, exhibiting boldness or chutzpah. 

  • Threatening in appearance or demeanor. 

adv
  • Extremely; very. 

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