idol vs lead vocalist

idol

noun
  • A popular entertainer, usually young, captivating and attractive, and often female, with an image of being close to fans. 

  • A cultural icon, or especially popular person. 

  • A graven image or representation of anything that is revered, or believed to convey spiritual power. 

lead vocalist

noun
  • A singer (or one of a small group of singers) who provides lead vocals to a song 

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