Synonyms of improbable

1 Syllable

slim, rare, weak

2 Syllables

dubious, reachy, flimsy, iffy, doubtful, fishy

3 Syllables

fanciful, handed-down, figmental, starry-eyed, far-fetched, farfetched, marvelous, nonviable, uncertain

4 Syllables

implausible, questionable, unconvincing, unthinkable, unhistoric, legendary, impractical, unsubstantial, incredible, unrealistic, nonrealistic, unlikely, infeasible

5 Syllables

unnegotiable, unhistorical, unverifiable, unconceivable, insupposable, ivory-tower, hundred-to-one, unserviceable, inconceivable, unbelievable

6 Syllables

unimaginable, inapprehensible, unbusinesslike