1. (a.) Not settled in opinion; undetermined; wavering; hesitating in belief; also used, metaphorically, of the body when its action is affected by such a state of mind; as, we are doubtful of a fact, or of the propriety of a measure.

2. (a.) Admitting of doubt; not obvious, clear, or certain; questionable; not decided; not easy to be defined, classed, or named; as, a doubtful case, hue, claim, title, species, and the like.

3. (a.) Characterized by ambiguity; dubious; as, a doubtful expression; a doubtful phrase.

4. (a.) of uncertain issue or event.

5. (a.) Fearful; apprehensive; suspicious.

Humean Pyrrhonic a bit thick a bit thin absurd agnostic ambiguous amoral arguable at issue beyond belief borderline chancy clouded confutable conjectural conscienceless contestable contingent controversial controvertible corrupt corrupted criminal crooked dark debatable deniable devious dishonest dishonorable disputable disreputable distrustful doubtable doubting dubious dubitable equivocal evasive felonious fishy fraudulent from Missouri hard of belief hard to believe hardly possible hazy hesitant hesitating iffy ill-got ill-gotten immoral implausible improbable in dispute in doubt in dubio in question inconceivable incredible incredulous indecisive indefinite indeterminate indirect insecure insidious leery mistakable mistrustful mistrusting moot more than doubtful not deserving belief not kosher obscure open open to doubt open to question open to suspicion passing belief precarious preposterous problematic queasy questionable questioning refutable ridiculous rocky rotten sceptical scrupulous shady shaky shameless shifty shy sinister skeptic skeptical slippery speculative staggering belief suppositional suspect suspecting suspicious tall thick thin tottery touch-and-go treacherous tricky unbelievable uncertain unclear unconscienced unconscientious unconscionable unconvinced unconvincing undecided undependable underhand underhanded unearthly uneasy unethical ungodly unhealthy unimaginable unlikely unpredictable unprincipled unpromising unreliable unresolved unsafe unsavory unscrupulous unsettled unsound unstable unsteady unstraightforward unsure unthinkable untrusting untrustworthy unworthy of belief vacillating vague wary without remorse without shame