plan vs purpose

plan

verb
  • To intend. 

  • To create a plan for. 

  • To design (a building, machine, etc.). 

  • To make a plan. 

noun
  • A drawing showing technical details of a building, machine, etc., with unwanted details omitted, and often using symbols rather than detailed drawing to represent doors, valves, etc. 

  • A subscription to a service. 

  • A set of intended actions, usually mutually related, through which one expects to achieve a goal. 

  • A method; a way of procedure; a custom. 

  • A two-dimensional drawing of a building as seen from above with obscuring or irrelevant details such as roof removed, or of a floor of a building, revealing the internal layout; as distinct from the elevation. 

purpose

verb
  • To have or set as one's purpose or aim; resolve to accomplish; intend; plan. 

  • To have (an) intention, purpose, or design; to intend; to mean. 

noun
  • meaning for existing or doing something. 

  • Resolution; determination. 

  • Function, role. 

  • The end for which something is done, is made or exists. 

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