He did not have all of the facts and did not want to prognosticate about what would happen. The word is used as a verb, and one of its synonyms is predict.
If you only use a word "once" in sentence, it only appears one time.
The man who was always once in this once in this once in that was frolicked by the amazement of the opocolips
Once bitten, twice shy.
The eggs will coagulate once they are fried.
Jessica became an angel once she died.
She was once an enemy but now she's a friend.
I thought of something that was the color of your eyes
Once A tornado hits it doesn't have PERMANENT damage.
"The army had to mobilise its forces quickly, once word came of the impending attack."
The gangs' graffiti desecrated the once-beautiful park wall.
the man became a renegade when he stole the stuff he once protected
A musical chord consists of multiple notes played at once.