free rider vs welfare parasite

free rider

noun
  • Someone who obtains goods or services legally without paying. 

  • A worker at an open shop who is able to enjoy the benefits negotiated by a union without being a member of the union. 

  • One who obtains benefit from a public good without paying for it directly. 

welfare parasite

noun
  • A person who is seen as living off the welfare of others. 

How often have the words free rider and welfare parasite occurred in a corpus of books? (source: Google Ngram Viewer )