An opinion or idea that is not based on definite knowledge and is formed by guessing.
Form an opinion or supposition about (something) on the basis of incomplete information.
The truth of his conjecture was confirmed by the newspaper report. (Oxford)
There's been a lot of conjecture in the media recently about the marriage.(Cambridge)
truth of his conjecture
a lot of conjecture
Assumption
Theory
Fact
Reality
Conjecturing