breather vs letup

breather

noun
  • A short break; a rest or respite. 

  • A spatially localized, time-periodic excitation in a one-dimensional lattice. 

  • An air inlet path to the crankcase 

  • Something or someone that breathes. 

  • A heavy breather. 

letup

noun
  • A pause or period of slackening. 

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