improbable

(a) not likely to be true or to occur or to have occurred
- legislation on the question is highly unlikely
- an improbable event
unlikely,
(s) having a probability too low to inspire belief unbelievable, unconvincing, unlikely,
(s) too improbable to admit of belief
- a tall story
marvelous, marvellous, tall,

unlikely unbelievable unconvincing marvelous marvellous tall

probable likely

improbably

improbableness