mild vs rigorous

mild

adj
  • Of only moderate severity; not strict. 

  • Not sharp or bitter; not strong in flavor. 

  • Not serious or dangerous. 

  • Moderately warm, especially less cold than expected. 

  • Gentle and not easily angered. 

  • Not overly felt or seriously intended. 

  • Acting gently and without causing harm. 

noun
  • A relatively low-gravity beer, often with a dark colour; mild ale 

rigorous

adj
  • Severe; intense. 

  • Showing, causing, or favoring rigour/rigor; scrupulously accurate or strict; thorough. 

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