1650s, "forecast of the probable course of a disease," from Late Latin prognosis, from Greek prognosis "foreknowledge," also, in medicine, "predicted course of a disease," from stem of progignoskein "come to know beforehand," from pro- "before" (see pro-) + gignoskein "come to know," from PIE root *gno- "to know." General (non-medical) use in English from 1706. A back-formed verb prognose is attested from 1837. Related: Prognosed; prognosing.
