The word sushi was borrowed in 1893 as American society slowly began a long history of adopting pieces of Japanese culture (after which it steadily grew in usage to a peak today). There's a misconception that the name has something to do with fish, but in the original Japanese, sushi actually meant "sour rice", in reference to the outside of the delicacy. Earlier, with a different character but the same pronunciation, that meant "sour" or "tasting of vinegar", and further back there was a word sounding like su, which just meant "vinegar". -Shi is an adjectival suffix tracing to the Heian period. The etymology of su is uncertain. There's a theory that takes it to Proto-Japonic and another going back to Chinese, so we're not even sure about the language family there. Still very interesting though!
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.