backup vs substituendum

backup

noun
  • A reserve or substitute. 

  • reinforcements 

  • A copy of a file or record, stored separately from the original, that can be used to recover the original if it is destroyed or damaged. 

  • An accumulation of material caused by a (partial) obstruction or (complete) blockage of the flow or movement of the material, or an accumulation of material that causes an overflow due to the flow being greater than the maximum possible flow. 

adj
  • Supporting, reinforcing; (music) of or related to accompaniment 

  • Standby, reserve or extra. 

  • That is intended as a backup. 

substituendum

noun
  • Something to be substituted or replaced. 

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