A parasite is often ingested alongside food, so is it really that surprising that the word itself means "beside food"? Because that's exactly the case. However, it's not for the reason I just listed. Originally, parasite only referred to humans who mooched off other humans, and got applied to other animals in the mere 1600s. So, through French parasite and Latin parasitus, the word traces back to the Ancient Greek word, which still meant the same thing, but literally could be defined as "one who eats at another's table". This is a portmanteau of the word para, meaning "beside" (from the Proto-Indo-European word per, with the same definition), and sitos, which meant "food" and has an unknown etymology. The idea is evident: a parasite is one who eats beside the host without reciprocating. Usage of parasite peaked in 1911 and has decreased since.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.