of uncertain outcome or result.

admitting of or causing doubt; uncertain; ambiguous.

unsettled in opinion or belief; undecided; hesitating.

of equivocal or questionable character

His tactics are highly doubtful.

adjective

certain , clear , confirmed , decided , definite , exact , resolved , settled , unquestionable , believing , confident , convinced , sure , trusting , implicit , unwavering

adjective

ambiguous , borderline , chancy , clouded , contingent , debatable , dicey , disreputable , doubtable , dubious , dubitable , equivocal , far-fetched , fat chance , fishy * , hazardous , hazy , iffy * , impugnable , inconclusive , indecisive , indefinite , indeterminate , indistinct , insecure , long shot * , obscure , on thin ice , open , pending , precarious , problematic , shady , sneaky * , speculative , suspect , suspicious , touch-and-go , touchy , uncertain , unconfirmed , undecided , uneasy , unsettled , unstable , unsure , up for grabsnotes:a person is capable of doubting , whereas a thing is dubitable ; dubious , unlike doubtful , carries the connotation of suspicion , agnostic , baffled , confused , discomposed , disconcerted , distracted , distrustful , disturbed , doubting , faithless , faltering , flustered , hesitant , hesitating , in a quandary , in clouds , in dilemma , irresolute , like doubting thomas , lost , not following , of two minds , perplexed , puzzled , questioning , skeptical , tentative , theoretical , troubled , unconvinced , unresolved , vacillating , wavering , without beliefnotes:a person is capable of doubting , problematical , questionable , unclear , improbable , unapt , unlikely , arguable , contested , disputable , exceptionable , moot , mootable , apprehensive , enigmatical , fearful , iffy , involved , shaky , undetermined , vague