parasite (păr′ə-sīt″)

noun

An organism that lives and feeds on or in an organism of a different species and causes harm to its host.

One who habitually takes advantage of the generosity of others without making any useful return.

One who lives off and flatters the rich; a sycophant.

A professional dinner guest, especially in ancient Greece.

Originally, one who frequents the tables of the rich and earns his welcome by flattery; hence a hanger-on; a fawning fiatterer; a sycophant.

Specifically In zoö., an animal that lives in or on and at the expense of another animal called technically the host; also, by extension, an animal which lives on or with, but not at the expense of, its host: in the latter sense, more precisely designated inquilince or commensal. Particularly, an insect which lives either upon or within another insect during its earlier stages, eating and usually destroying its host.In botany, a plant which grows upon another plant or upon an animal, and feeds upon its juices.

In teratology

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.