not definitely ascertainable or fixed, as in time of occurrence, number, dimensions, or quality.

not confident, assured, or free from hesitancy

an uncertain smile.

not clearly or precisely determined; indefinite; unknown

a manuscript of uncertain origin.

vague; indistinct; not perfectly apprehended

an abstruse novel with uncertain themes.

subject to change; variable; capricious; unstable

a person of uncertain opinions.

ambiguous; unreliable; undependable

Her loyalties are uncertain.

dependent on chance or unpredictable factors; doubtful; of unforeseeable outcome or effect.

unsteady or flickering, as light; of changing intensity or quality.

adjective

certain , clear , definite , determined , foreseeable , secure , sure , unchanging

adjective

ambiguous , ambivalent , chancy , conjectural , dubious , erratic , fitful , hanging by a thread , hazy , hesitant , iffy * , incalculable , inconstant , indefinite , indeterminate , indistinct , insecure , irregular , irresolute , on thin ice , precarious , questionable , risky , speculative , touch and go , unclear , unconfirmed , undecided , undetermined , unfixed , unforeseeable , unpredictable , unreliable , unresolved , unsettled , unsure , up for grabs , up in the air , vacillating , vague , variable , wavering , borderline , clouded , doubtful , dubitable , equivocal , inconclusive , indecisive , problematic , problematical , arguable , contested , disputable , exceptionable , moot , mootable , cloudy , inexplicit , nebulous , obscure , suspect , suspicious , open , skeptical , alterable , fluid , mutable , unstable , unsteady , variant , changeable , fantastic , fantastical , fickle , freakish , inconsistent , mercurial , temperamental , ticklish , volatile , whimsical , amphibolic , asea , capricious , contingent , controversial , distrustful , enigmatical , fallible , flickering , hesitating , iffy , improbable , penumbral , tentative , touch-and-go , unformalized , visionary