Meaning

noun 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 a follower who hangs around a host (without benefit to the host) in hope of gain or advantage

originFrom 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”).

Etymology from Wiktionary, CC BY-SA 3.0