Definition of undecidable
: not capable of being decided : not decidable … a huge popular audience, most of whom must have been baffled and exasperated by its elaborate and undecidable mystifications.— David Lodge … deconstruction, which teaches that literature is essentially "undecidable," beyond interpretation …— James Atlas To be complete such a system must be able to prove that any formula expressible in its language (a mathematical equation, for example, or a statement in symbolic logic) is either true or false; nothing can be undecidable.— George Johnson
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The first known use of undecidable was in 1640
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