1. The condition of being uncertain; doubt.
2. Something uncertain: the uncertainties of modern life.
3. Statistics The estimated amount or percentage by which an observed or calculated value may differ from the true value.

Synonyms: These nouns refer to the condition of being unsure about someone or something. Uncertainty, the least forceful, merely denotes a lack of assurance or conviction: I regarded my decision with growing uncertainty.
Doubt and dubiety imply a questioning state of mind: "Doubt is part of all religion" (Isaac Bashevis Singer). On this point there can be no dubiety.
Skepticism generally suggests an instinctive or habitual tendency to question and demand proof: "A wise skepticism is the first attribute of a good critic" (James Russell Lowell).
Suspicion is doubt as to the innocence, truth, integrity, honesty, or soundness of someone or something: His furtiveness aroused my suspicions.
Mistrust denotes lack of trust or confidence, as in a person's motives, arising from suspicion: The staff viewed the consultant's hasty recommendations with mistrust.