- 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.
- not able to be accurately known or predictedthe issue is uncertain
- (when postpositive, often foll by of) not sure or confident (about)a man of uncertain opinion
- not precisely determined, established, or decideduncertain plans
- not to be depended upon; unreliablean uncertain vote
- liable to variation; changeablethe weather is uncertain
- in no uncertain terms
adj.c.1300, “of indeterminate time or occurrence,” from un- (1) “not” + certain (adj.). Meaning “not fully confident” is recorded from late 14c. (implied in uncertainty). Related: Uncertainly. see in no uncertain terms.