second string vs stand-in

second string

noun
  • A unit of players which is considered to have a secondary level of talent and which usually plays after the first string. 

adj
  • Not as good; of a lower quality or condition. 

stand-in

noun
  • A person of similar size and shape to an actor who "stands in" for that actor during the lengthy process of setting up a shot, but who, unlike a double, does not appear in the film. 

  • A substitute. 

How often have the words second string and stand-in occurred in a corpus of books? (source: Google Ngram Viewer )