Synonym of unbelievable

incredible amazing extraordinary astonishing great enormous mind-boggling implausible impossible improbable inconceivable outlandish preposterous too much unimaginable unthinkable beyond belief cockamamie cockeyed doubtful dubious far-fetched fishy flaky flimsy for the birds full of holes harebrained incogitable kooky lamebrained open to doubt past belief phony questionable reaching scatterbrained screwy staggering suspect thick thin unconvincing unsubstantial weak won't hold water won't wash

fantastic unlikely fanciful unreal