improbable

Not likely to be true.

Adjective

Not likely to be true.
- It's highly improbable that aliens abducted you.
- Improbabile, that cannot be prooued, improbable. - 1598, John Florio, “Improbabile”, in A Worlde of Words, or Most Copious, and Exact Dictionarie in Italian and English, […], London: […] Arnold Hatfield for Edw[ard]...
- Nay, if he be of a proud humour, […] he will not Bate an Ace of abſolute certainty, but however doubtful or improbable the thing is, coming f[r]om him it muſt go for an indiſputable truth. - 1674, [Richard Allestree],...
Not likely to happen.
- Due to the loss of power, it is improbable that we will begin on time.

Borrowed from Latin improbābilis. By surface analysis, im- + probable.