A crystal ball is the glass sphere used to see the future. Gaze into the crystal ball, no crystal ball, the crystal ball says.
The figurative use is much the commoner, and saying you have no crystal ball is how anybody declines to predict something. The practice is called scrying and long predates the fairground image.
1nouncrystal ballThe glass sphere used to see the future.
“The fortune-teller gazed into her crystal ball and told me I'd meet a stranger.”
crystal ball is an object.
Practised in Myths & Legends, Fairy Tales & Folklore