Origin and usage
The noun parasite is borrowed from the Latin ‘parasitus‘, which itself came from a Greek word meaning ‘someone who eats at another person’s table’. It was first recorded in English in the 16th century with the meaning given above. The biological meaning came later, in the 18th century.
The recent success of the Korean film Parasite at the Oscars, where it became the first foreign language film ever to win the award for Best Picture, has brought the term parasite into the spotlight. The Macmillan Dictionary entry puts the meaning referred to in the film’s title first, with the biological sense second. This is because in current, non-specialist English this meaning is more frequent. This meaning is labelled ‘showing disapproval’: you only refer to someone as a parasite if you think that what they are doing is wrong. Biological parasites need a host and of course the same could be said of human parasites, even if in the case of humans it is not always clear who is the parasite and who the host. There is a related adjective parasitic (or parasitical) and a verb, parasitize. Both of these are more frequently used in biological contexts.
bloodsucker, freeloader, leech, sponger