frivolous vs mysterious

frivolous

adj
  • Silly, especially at an inappropriate time or in an inappropriate manner. 

  • Having no reasonable prospect of success because its claim is without merit, lacking a supporting legal or factual basis, while the filing party is, or should be, aware of this. 

  • Of little weight or importance; not worth notice; slight; trivial. 

mysterious

adj
  • Deliberately evasive or enigmatic. 

  • Difficult to understand. 

  • Having unknown qualities. 

  • Of unknown origin. 

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