digression vs irregularity

digression

noun
  • An elongation, a deflection or deviation from a mean position or expected path. 

  • An aside, an act of straying from the main subject in speech or writing. 

  • The act of straying from the main subject in speech or writing, (rhetoric) particularly for rhetorical effect. 

irregularity

noun
  • The state or condition of being irregular, or the extent to which something is irregular. 

  • A violation of rules. 

  • An object or event that is not regular or ordinary. 

  • An instance of being irregular. 

  • Irregular bowel movement (e.g. diarrhea or constipation). 

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