surmise
Definitions
A supposition that something may be true, even though there is no evidence to confirm it.
To infer or guess that something is the case without having certain proof.
Examples
From the look on her face, I could only surmise that she was disappointed with the results.
The detective began to surmise that the thief had inside information about the security system.
It is difficult to surmise the true intentions of someone you have only just met.