develop vs extend

develop

verb
  • To advance; to further; to promote the growth of. 

  • To progress through a sequence of stages. 

  • To bring out images latent in photographic film. 

  • To acquire something usually over a period of time. 

  • To place one's pieces actively. 

  • To change with a specific direction, progress. 

  • To create. 

  • To cause a ball to become more open and available to be played on later. Usually by moving it away from the cushion, or by opening a pack. 

  • To change the form of (an algebraic expression, etc.) by executing certain indicated operations without changing the value. 

extend

verb
  • To increase in extent. 

  • To reenlist for a further period. 

  • To increase in quantity by weakening or adulterating additions. 

  • To value, as lands taken by a writ of extent in satisfaction of a debt; to assign by writ of extent. 

  • To straighten (a limb). 

  • Of a class: to be an extension or subtype of, or to be based on, a prototype or a more abstract class. 

  • To cause to increase in extent. 

  • To cause to last for a longer period of time. 

  • To possess a certain extent; to cover an amount of space. 

  • To bestow; to offer; to impart; to apply. 

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