free rider vs vampire

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. 

vampire

noun
  • A person who drains one's time, energy, money, etc. 

  • A medical technician who works with patients' blood. 

  • A person with the medical condition systemic lupus erythematosus, colloquially known as vampirism, with effects such as photosensitivity and brownish-red stained teeth. 

  • Synonym of anti-ship missile (ASM), particularly an incoming hostile one. 

  • A blood-sucking bat; vampire bat (Desmodus rotundus) 

  • A mythological undead creature said to feed on the blood of the living. 

verb
  • To drain of energy or resources. 

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