The cashew nut was originally endemic solely to northeastern Brazil, and before the Europeans came to spread it to the rest of the world it was only known to a few people groups living in the Amazon River Basin. One of those peoples, the Tupians, referred to the cashew as acajuba, which in their language meant "nut that produces itself". Where that word comes from is unknown, because the language wasn't recorded, but it possibly traces back to a Je-Tupi-Carib proto-language and an urheimat in what is today the Brazilian state of Rodôndia. Fast forwarding thousands of years, when the Portuguese discovered the nut from the natives and brought it back home, they needed a word for the new delicacy, so they just used a slight variation of the one the Tupians had been using, acaju. As the nut traveled northward, this was brought into French as acajou, and the British, shortening the French word and misinterpreting the ending, mangled the spelling into cashew as we know it today.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd