means An organism that lives on or inside another, drawing nourishment at the host's expense — or, by extension, a person who lives off others without contributing.

from From Greek 'parasitos,' literally 'beside the grain' (para 'beside' + sitos 'food, grain'). In ancient Greece a parasitos originally meant a respectable dinner guest, even an official who ate at the temple table — but the word slid downhill into 'one who flatters his way to a free meal.' Latin borrowed it as 'parasitus,' the sponging hanger-on of Roman comedy, and only in the 1700s did naturalists draft the word into biology for creatures that mooch off a living host.