THESAURUS
unbelievable
a bit thick, a bit thin, absurd, antic, beyond belief, doubtable, doubtful, dubious, dubitable, fanciful, fantastic, flimsy, hard of belief, hard to believe, implausible, impossible, improbable, incomprehensible, inconceivable, incredible, mind-boggling, not deserving belief, open to doubt, open to suspicion, passing belief, preposterous, problematic, questionable, ridiculous, staggering belief, suspect, suspicious, tall, thick, thin, unaccountable, unconvincing, unearthly, unexpected, ungodly, unimaginable, unsubstantial, unthinkable, unworthy of belief, weak
ROGET THESAURUS
unbelievable
Doubt
N
unbelief doubt, unbelief, disbelief, misbelief, discredit, miscreance, infidelity, dissent, change of opinion, retraction, doubt, skepticism, scepticism, misgiving, demure, distrust, mistrust, cynicism, misdoubt, suspicion, jealousy, scruple, qualm, onus probandi, incredibility, incredibleness, incredulity, doubter, skeptic, cynic, unbeliever, unbelieving, skeptical, sceptical, incredulous as to, skeptical as to, distrustful as to, shy as to, suspicious of, doubting, doubtful, disputable, unworthy of, undeserving of belief, questionable, suspect, suspicious, open to suspicion, open to doubt, staggering, hard to believe, incredible,
unbelievable, not to be believed, inconceivable, impossible, fallible, undemonstrable, controvertible, cum grano salis, with a grain of salt, with grains of allowance, fronti nulla fides, nimium ne crede colori, timeo Danaos et dona ferentes, I fear the Greeks even when bearing gifts, beware of Greeks bearing gifts, credat Judaeus Apella, let those believe who may, ad tristem partem stenua est suspicio.