birr vs churr

birr

verb
  • To make a whirring noise; make a noise like that of revolving wheels, or of millstones at work. 

  • To lurch or set to spinning. 

noun
  • The currency of Ethiopia, divided into 100 santims. 

  • A strong trilling. 

  • The force of movement; rush, impetus, momentum, driving force 

  • A whirring noise 

  • strength, vigor, energy 

churr

verb
  • To make the low vocal sound of some birds. 

noun
  • A low vocal sound made by some birds. 

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