first name vs sobriquet

first name

noun
  • The first element of a full name in cultures that place the given name first. 

sobriquet

noun
  • A familiar name for a person or thing; a nickname (sometimes assumed by the person, but often given by others), that is descriptive. 

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