irregularity vs usual

irregularity

noun
  • 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). 

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

usual

noun
  • A specific good or service (e.g. a drink) that someone typically orders. 

  • The typical state of something, or something that is typical. 

adj
  • Most commonly occurring; typical. 

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