The best replacement for prediction is hypothesis.

The best alternatives to prediction are rated as following:
★★★★★  hypothesis
★★★★  inference
★★★  forecast
★★  explanation
★★  projection
★★  prophecy
★  classification
★  assumption
★  estimation
★  causation
  observation
  guess
  forecasting
  causality
  prognosis
  earthquake forecasting
  clinical prediction
  revise hypothesis

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Speaking about prediction, one probably shouldn't forget about old wives tales.

Other search terms related to prediction and their ratings are:
★★★★★ old wives tales
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