fad vs vagary

fad

noun
  • A phenomenon that becomes popular for a very short time. 

vagary

noun
  • An erratic, unpredictable occurrence or action. 

  • Something vague. 

  • An impulsive or illogical desire; a caprice or whim. 

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