crystal ball
noun
°A globe of glass or crystal used to foretell the future.
"Oh, crystal ball, crystal ball, / Save us all, tell me life is beautiful, / Mirror, mirror on the wall."
°(by extension, used mostly in the negative form) A way of seeing into the future.
"If her past is a crystal ball to her future, she will perhaps never be rich, even though she is a good, kind, educated, hard-working person."
synonyms: showstone, shew stone