retrofit vs strengthen

retrofit

verb
  • To give new characteristics or make alterations (to someone or something) to suit them to changed circumstances. 

  • To supply (a device, structure, etc.) with new components or parts that were not previously available or installed; to modernize. 

  • Synonym of backport (“to retroactively supply a fix or feature to a previous version of a software product at the same time or after supplying it to the current version.”) 

  • To supply a device, structure, etc., with new components or parts that were not previously available or installed. 

  • To add or substitute (new components or parts) that were not previously available for or installed in a device, structure, etc. 

noun
  • An act of supplying a device, structure, etc., with new components or parts that were not previously available or installed; a retrofitting. 

  • A change made to a device, structure, etc., by introducing components or parts that were not previously available or installed. 

strengthen

verb
  • To reinforce, to add to, to support (someone or something) 

  • To make strong or stronger; to add strength to; to increase the strength of; to fortify. 

  • To empower; to give moral strength to; to encourage; to enhearten. 

  • To grow strong or stronger. 

  • To substantiate; to corroborate (a belief, argument, etc.) 

  • To augment; to improve; to intensify. 

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