apprentice vs sidekick

apprentice

noun
  • One who is bound by indentures or by legal agreement to serve a tradesperson, or other person, for a certain time, with a view to learn the art, or trade, in which his master is bound to instruct him. 

  • A trainee, especially in a skilled trade. 

verb
  • To put under the care and supervision of a master, for the purpose of instruction in a trade or business. 

  • To be an apprentice to. 

sidekick

noun
  • An assistant to another person, especially to a superior or more important person. 

  • In literature, theatre/theater, etc., a good foil of the protagonist, a character who helps emphasize the traits of the main character. 

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