Parasite (noun)

1. An organism that lives in or on another organism (its host) and benefits by deriving nutrients at the host's expense.
2. A person who habitually relies on or exploits others and gives nothing in return.

Origin:

From the greek word "parasitos" meaning "one who eats at another"s table".

Examples:

1. The tapeworm is a common parasite found in the human intestine.
2. Many parasites are harmless to their host, while others can cause serious health problems.
3. He was a parasite who had been living off his parents for years.
4. She was a parasite who always took advantage of her friends' generosity.
5. The company's profits were being drained by the parasitic practices of the subsidiary.