Before Arcane, this question was unanswered. But now we know that her name was given to her by her sister, but not directly. A friend of theirs, Milo, called Powder “Jinx” because she was bad luck on their missions. At first, her sister, Vi, defended her. However, after a terrible accident that got their friends killed, Vi told Powder that Milo was right, she was bad luck. Since then, Jinx was born as a twisted acknowledgment of her bad luck nature.