improbable

adj

1.
not likely to be true or to occur or to have occurred
unlikely
Antonym:
probable
Derived from:
improbability improbableness
2.
having a probability too low to inspire belief
unbelievable unconvincing unlikely
Derived from:
improbableness
3.
too improbable to admit of belief
marvellous marvelous tall
Derived from:
improbableness