Im·prōb'a·ble, a.

a. [Fr. & Sp. improbable, It. improbabile, Lat. improbabilis; prefix im, for in, not, and probabilis, probable.] Not probable; unlikely to be true; not to be expected under the circumstances of the case; as, an improbable story or event. He . . . sent an improbable letter, as some of the contents discover. Milton.