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.