'Parasite' meant 'banquet freeloader' in Greek — a social insult before it became a biological term.
An organism that lives in or on another organism (its host), deriving nutrients at the host's expense; figuratively, a person who exploits the generosity of others without giving anything in return.
From Latin 'parasitus,' from Greek 'parasitos' (one who eats at the table of another), from 'para-' (beside) + 'sitos' (food, grain). The original Greek meaning was social, not biological: a 'parasitos' was a person who dined at another's table, a professional dinner guest or flatterer who earned meals through wit and obsequiousness. Greek comedy made the 'parasitos' a stock character — the hungry hanger-on. The biological sense, applied
The original Greek 'parasitos' was not an insect or worm but a professional dinner guest — a stock character in Greek comedy who earned free meals by flattering his host. The biological meaning came two thousand years later, when scientists noticed that certain organisms did exactly the same thing, but with blood instead of banquet food.