uncertain

UK: /ʌnˈsɜː^rt^ən/ US: /ʌnˈsɝtən/ ,(un sûr′tn)

WordReference Random House Learner's Dictionary of American English © 2025

un•cer•tain /ʌnˈsɜrtən/   adj. 

1. not known precisely;
   not fixed:
   The size of the deficit is uncertain.
2. not confident or assured;
   hesitant:
   an uncertain smile.
3. not clearly determined;
   unknown:
   a manuscript of uncertain origin.
4. likely to change;
   unstable:
   The weather pattern for the next few days is uncertain.

un•cer•tain•ly, adv. 
un•cer•tain•ty, n., pl. -ties. 

[uncountable] He showed uncertainty of manner.

[countable] life's uncertainties.

WordReference Random House Unabridged Dictionary of American English © 2025

un•cer•tain  (un sûr′tn), adj. 

1. not definitely ascertainable or fixed, as in time of occurrence, number, dimensions, or quality.
2. not confident, assured, or free from hesitancy:
   an uncertain smile.
3. not clearly or precisely determined;
   indefinite;
   unknown:
   a manuscript of uncertain origin.
4. vague;
   indistinct;
   not perfectly apprehended:
   an abstruse novel with uncertain themes.
5. subject to change;
   variable;
   capricious;
   unstable:
   a person of uncertain opinions.
6. ambiguous;
   unreliable;
   undependable:
   Her loyalties are uncertain.
7. dependent on chance or unpredictable factors;
   doubtful;
   of unforeseeable outcome or effect.
8. unsteady or flickering, as light;
   of changing intensity or quality.

• 1250–1300; Middle English; see un-¹, certain

un•cer′tain•ly, adv. 
un•cer′tain•ness, n. 
Synonyms

• 1. unsure, unpredictable.
  Uncertain, insecure, precarious imply a lack of predictability. That which is uncertain is doubtful or problematical; it often involves danger through an inability to predict or to place confidence in the unknown:
  The time of his arrival is uncertain.
  That which is insecure is not firm, stable, reliable, or safe, and hence is likely to give way, fail, or be overcome:
  an insecure foundation, footing, protection.
  Precarious suggests great susceptibility to failure, or exposure to imminent danger:
  a precarious means of existence.
• 3. unsettled, undetermined.
• 8. irregular.

Collins Concise English Dictionary © HarperCollins Publishers::

uncertain / ʌnˈsɜːt^ən/ adjective

1. not able to be accurately known or predicted: the issue is uncertain
2. when postpositive, often followed by of: not sure or confident (about): a man of uncertain opinion
3. not precisely determined, established, or decided: uncertain plans
4. not to be depended upon; unreliable: an uncertain vote
5. liable to variation; changeable: the weather is uncertain
6. in no uncertain terms ⇒ unambiguously
7. forcefully

unˈcertainly adverb