cast iron vs improper

cast iron

adj
  • Inflexible or without exception. 

  • Made of cast iron. 

  • Durable; tough; resilient. 

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

improper

adj
  • unsuitable to needs or circumstances; inappropriate; inapt 

  • Not properly named; See, for example, improper fraction 

  • Not in keeping with conventional mores or good manners; indecent or immodest 

  • Not consistent with established facts; incorrect 

  • Of a complex random variable, correlated with its conjugate 

  • Not according to facts; inaccurate or erroneous 

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