Collocation

• Collocation a word or phrase which is frequently used with another word or phrase, in a way that sounds correct to people who have spoken the language all their lives, but might not be expected from the meaning:
  
  Collocations with research are such as
  Market research
  Operational research
  Research and development
  research
  research project
  
• Collocations with purpose are such as
  express purpose
  ecological purpose
  travelling purpose
  multi purpose
  development purpose