letup vs solemnity

letup

noun
  • A pause or period of slackening. 

solemnity

noun
  • A solemn or formal observance; proceeding according to due form; the formality which is necessary to render a thing done valid. 

  • A feast day of the highest rank celebrating a mystery of faith such as the Trinity, an event in the life of Jesus, the Virgin Mary, or another important saint. 

  • An instance or example of solemn behavior; a rite or ceremony performed with reverence. 

  • The quality of being deeply serious and sober or solemn. 

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