initials vs nickname

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 

nickname

noun
  • A familiar, shortened or diminutive name for a person or thing. 

  • A familiar, invented name for a person or thing used instead of the actual name of the person or thing, often based on some noteworthy characteristic. 

verb
  • To give a nickname to (a person or thing). 

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