idiosyncrasy vs irregularity

idiosyncrasy

noun
  • A language or behaviour that is particular to an individual or group. 

  • A peculiar individual reaction to a generally innocuous substance or factor. 

  • A peculiarity that serves to distinguish or identify. 

  • A behavior or way of thinking that is characteristic of a person. 

irregularity

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

  • A violation of rules. 

  • 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. 

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