dead calm vs vain

dead calm

adj
  • Completely still with no waves and no wind. 

noun
  • The condition of a perfectly flat sea with no waves and no wind. 

vain

adj
  • Having no real substance, value, or importance; empty; void; worthless; unsatisfying. 

  • Overly proud of oneself, especially concerning appearance; having a high opinion of one's own accomplishments with slight reason. 

  • Showy; ostentatious. 

  • Effecting no purpose; pointless, futile. 

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