supposition
Definitions
An uncertain belief or an idea held without proof.
The act of assuming something to be true.
Examples
His entire argument was based on the false supposition that the company was failing.
The detective worked under the supposition that the thief was still inside the building.
It is a common supposition that wealth leads to happiness, but that is not always the case.
Synonyms
assumption conjecture hypothesis surmise presumption theory speculation