The word rhubarb was borrowed into English as Rubarbe in the late fourteenth century. Other spellings around that time included reubarbe, rubarb, reubard, reuballe, and more. Through Old French rubarbe, the word comes from Medieval Latin reubarbum and Ancient Greek rha barbaron, which meant "foreign rhubarb" (a wonderfully recursive etymology). You'll notice that the h appears in Greek but is only a recent readdition to English: the letter was inserted throughout Middle English and then standardized in the eighteenth century because of influence of the rheum plant genus. The rha part of rha barbaron is an ancient Scythian name of the Volga River, from whence the vegetable was commonly important, and the barbaron is the same element as in the word barbarian - it was basically use as a negative term for anybody who was not Greek. Finally, barbaron is onomatopoeic of what unintelligible foreign speech sounded like to the Greeks.
Hello! I'm Adam Aleksic, a junior studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy trivia, politics, vexillology, geography, board games, conlanging, art history, and law.