IMPROBABLE
improbable, marvelous, marvellous, tall
(adjective) too improbable to admit of belief; “a tall story”
improbable, unlikely
(adjective) not likely to be true or to occur or to have occurred; “legislation on the question is highly unlikely”; “an improbable event”
improbable, unbelievable, unconvincing, unlikely
(adjective) having a probability too low to inspire belief
Source: WordNet® 3.1
Etymology
Adjective
improbable (comparative more improbable, superlative most improbable)
Not likely to be true.
Not likely to happen.
Antonyms
• probable
Source: Wiktionary
Im*prob"a*ble, a. Etym: [L. improbabilis; pref. im- not + probabilis
probable: cf. F. improbable. See Probable.]
Definition: 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. Milton.
– Im*prob"a*ble*ness, n.
– Im*prob"a*bly, adv.
Source: Webster’s Unabridged Dictionary 1913 Edition