prognosticate (v.)

"foretelling or foreshadowing of future events by present signs," especially "act of making a medical prognosis," late 14c., pronasticacioun, from Old French pronosticacion (14c.) and directly from Medieval Latin *prognosticationem (nominative prognosticatio), noun of action from past-participle stem of prognosticare "foretell," from Latin prognostica "sign to forecast weather," from neuter plural of Greek prognōstikos "foreknowing," from progignōskein "come to know beforehand" (see prognosis). The -g- was restored in the English word 16c.

1650s, "forecast of the probable course and termination of a case of a disease," from Late Latin prognosis, from Greek prognōsis "foreknowledge," also, in medicine, "predicted course of a disease," from stem of progignōskein "come to know beforehand," from pro- "before" (see pro-) + gignōskein "come to know" (from PIE root *gno- "to know").

An earlier form in the same sense was pronostike (early 15c.), from Medieval Latin pronosticum. The general (non-medical) sense of "a forecast of the course of events" in English is from 1706. A back-formed verb prognose is attested from 1837; the earlier verb was Middle English pronostiken (c. 1400), from Medieval Latin pronosticare.  Related: Prognosed; prognosing.

"a foreknower or foreteller of future events by present signs, a soothsayer," 1550s, agent noun in Latin form from prognosticate.