noun (n)

• an animal or plant that lives in or on a host (another animal or plant); it obtains nourishment from the host without benefiting or killing the host(noun.animal)

  Antonym:
  host
  

  source: wordnet30
• a follower who hangs around a host (without benefit to the host) in hope of gain or advantage(noun.person)

  Synonym:
  leech, sponge, sponger
  

  source: wordnet30
• One who frequents the tables of the rich, or who lives at another's expense, and earns his welcome by flattery; a hanger-on; a toady; a sycophant.(noun)

  source: webster1913