cognomen vs initials

cognomen

noun
  • A nickname or epithet by which someone is identified. 

  • The third part of the name of a citizen of Ancient Rome. 

  • Surname. 

initials

noun
  • An abbreviation of a person's name, constructed by taking the initial letters of first, last, and sometimes middle name(s). See monogram 

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