fill-in vs second string

fill-in

noun
  • Something added to fill a gap. 

  • A substitution. 

  • An intermediate result that must be stored temporarily during the course of a sparse matrix computation. 

  • A temporary replacement for another, especially at a job. 

  • A musical embellishment (usually percussion) that is added to connect musical phrases. 

  • A product category that is used to complete a range or variety of a product line. 

  • Something added to increase the size of something; padding or filler. 

  • A question or puzzle in which one is expected to fill in a missing part of something. 

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. 

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