dead calm vs insubstantial

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. 

insubstantial

adj

  • Lacking substance; not real or strong. 

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