stammer vs vox

stammer

noun
  • The involuntary repetition of a sound in speech. 

  • A speech defect whereby someone speaks with a stammer 

verb
  • To utter with a stammer, or with timid hesitancy. 

  • To keep repeating a particular sound involuntarily during speech. 

vox

noun
  • The voice, especially one's singing voice; vocals. 

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