parasite
n. countablen. an animal or plant that lives on or inside another living thing and gets its food from it. It can also describe a person who takes support from others without giving anything back.
n. an organism that lives in or on an organism of another species and benefits by deriving nutrients at the other's expense. In a social context, refers to a person who habitually relies on or exploits others.
The tick is a common parasite that feeds on blood.
Doctors found that the patient's fatigue was caused by a parasite he contracted from drinking untreated water.
In the natural world, the relationship between a parasite and its host is often a delicate evolutionary race where the host develops defenses while the intruder finds new ways to bypass them.
From Middle French parasite, from Latin parasitus, from Ancient Greek παράσιτος (parásitos, “person who eats at the table of another”), from noun use of adjective meaning "feeding beside", from παρά (pará, “beside”) + σῖτος (sîtos, “food”).
Often used metaphorically in political or social criticism to describe individuals or institutions perceived as exploitative.