Improbable
Improbable , adjective
[Latin improbabilis; pref. im- not + probabilis probable: compare French improbable. See Probable.]
Not probable; unlikely to be true; not to be expected under the circumstances or in the usual course of events; as, an improbable story or event.
He... sent to Elutherius, then bishop of Rome, an improbable letter, as some of the contents discover.