dead calm vs shoal

dead calm

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

adj
  • Completely still with no waves and no wind. 

shoal

noun
  • A shallow in a body of water. 

  • A sandbank or sandbar creating a shallow. 

  • A large number of fish (or other sea creatures) of the same species swimming together. 

  • Any large number of persons or things. 

verb
  • To become shallow. 

  • To arrive at a shallow (or less deep) area. 

  • To collect in a shoal; to throng. 

  • To cause a shallowing; to come to a more shallow part of. 

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