expansion vs improvement

expansion

noun
  • An act, process, or instance of expanding. 

  • A new addition. 

  • A product to be used with a previous product. 

  • That which is expanded; expanse; extended surface. 

  • The operation of steam in a cylinder after its communication with the boiler has been cut off, by which it continues to exert pressure upon the moving piston. 

  • The replacement of a short name (e.g., acronym, initialism, alphanumeric symbol, abbreviation) with the longer name that is synonymous with it, as when spelling out acronyms to ensure clarity for a general audience. 

  • The string of text thus substituted. 

  • The fractional change in unit length per unit length per unit temperature change. 

improvement

noun
  • The act of improving; advancement or growth; a bettering 

  • Increase; growth; progress; advance. 

  • Something which is improved 

  • Valuable additions or betterments, for example buildings, clearings, drains, fences, etc., on premises. 

  • A useful addition to, or modification of, a machine, manufacture, or composition. 

  • The state of being improved; betterment; advance 

  • The act of making profitable use or application of anything, or the state of being profitably employed; practical application, for example of a doctrine, principle, or theory, stated in a discourse. 

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