unguessable

/ʌnˈɡɛsəbəl/
adjective
  1. Impossible to guess or figure out; not able to be predicted or known.
    • The outcome of the election seemed unguessable until the very last votes were counted.
    • Her next move in the game was unguessable, keeping everyone on edge.
    • The answer to the riddle was completely unguessable, even for the smartest students.
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