The story
From magic + eight-ball (“a billiard ball, almost always black, bearing the number eight”), due to the toy's design.
Etymology from Wiktionary, CC BY-SA 4.0.
Magic 8 Ball
Today it means: A novelty toy manufactured by Mattel that is a plastic sphere resembling an oversized eight ball with a small digital screen on its opposite side that, when shaken, reveals a response to a yes or no question. Full definition →