bit part vs role

bit part

noun
  • A minor role, generally not assigned a name. 

role

noun
  • Designation that denotes an associated set of responsibilities, knowledge, skills, and attitudes 

  • In the Raku programming language, a code element akin to an interface, used for composition of classes without adding to their inheritance chain. 

  • The function of a word in a phrase. 

  • An ancient unit of quantity, 72 sheets of parchment. 

  • A character or part played by a performer or actor. 

  • The expected behaviour of an individual in a society. 

  • The function or position of something. 

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