irregularity vs quirk

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. 

quirk

noun
  • An idiosyncrasy; a slight glitch, mannerism; something unusual about the manner or style of something or someone. 

  • An acute angle dividing a molding; a groove that runs lengthwise between the upper part of a moulding and a soffit. 

verb
  • To (cause to) move with a wry jerk. 

  • To furnish with a quirk or channel. 

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