infrequency vs nonregularity

infrequency

noun
  • The state of being unfrequented; isolation; seclusion. 

  • The characteristic of being infrequent. 

nonregularity

noun
  • The state or condition of being nonregular. 

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