Synonyms of unbelievable

1 Syllable

thick, thin, weak

2 Syllables

kooky, dubious, screwy, reachy, phony, flimsy, unreal, doubtful, reaching, flaky, cockeyed, fishy, suspect, turn-on

3 Syllables

amazing, storybook, fantastic, far-fetched, foolheaded, outlandish, doubtable, marvelous, staggering, obscurer, unheard-of, fabulous

4 Syllables

unrenowned, unspeakable, implausible, questionable, unconvincing, lamebrained, unthinkable, impossible, ridiculous, fantastical, preposterous, improbable, cockamamie, unsubstantial, incredible, harebrained, astonishing, miraculous, unlikely, scatterbrained, wonderworking

5 Syllables

undescribable, incogitable, unconceivable, insupposable, unutterable, hundred-to-one, inexpressible, inconceivable, indefinable

6 Syllables

unimaginable, inapprehensible, incommunicable