disfluency vs fluency

disfluency

noun
  • Lack of fluency in speech; any of various breaks, irregularities, and non-lexical vocables that occur within otherwise fluent speech. 

fluency

noun
  • The quality of being fluent in a language; A person's command of a particular language. 

  • The quality of smoothness of flow. 

  • The quality of consistently applying skill correctly in the manner of one well-practiced at it, requiring little deliberate thought to perform without mistakes 

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