Is it ensure, insure, or assure?
late 14c., "to scheme," from fore- "before" + casten "contrive." Meaning "predict events" first attested late 15c. Related: Forecasted; forecasting.
early 15c., probably from forecast (v.); earliest sense was "forethought, prudence;" meaning "conjectured estimate of a future course" is from 1670s. A Middle English word for weather forecasting was aeromancy.