If you come down with an illness, you might ask your doctor what your prognosis is. A prognosis is a prediction about the course of a disease.
Prognosis comes from the Greek pro- "before" and gnosis "knowledge." It means to know beforehand, but keep in mind that it is only a probable outcome and not a sure thing. Financial analysts frequently change their prognosis of the economy as they hear each piece of good or bad economic news. And if the weather prognosis is sunny and dry, but you see dark clouds forming, you would be wise to pack an umbrella.