(with "the") Something uncertain.

Not certain; unsure. / Not known for certain; questionable. / Not yet determined; undecided. / Variable and subject to change. / Fitful or unsteady. / Unpredictable or capricious.

Misspelling of uncertainty.

The quality of being uncertain.

(idiomatic) (of a statement, especially a threat or admonishment) Bluntly, forthrightly; explicitly, categorically.

In an uncertain manner.

(uncountable) Doubt; the condition of being uncertain or without conviction. / (countable) Something uncertain or ambiguous.

(quantum mechanics) The Heisenberg uncertainty principle.

(cricket) The area near the batsman's off stump where, if a ball passes that area, the batsman is unsure whether to play it (and risk an edge) or leave it (and risk being bowled).

(physics, quantum mechanics) The principle that there is an absolute limit on the combined accuracy of certain pairs of simultaneous, related measurements, especially that of the position and momentum of a particle. Originally posited as a problem of measurement, it was soon refined as an inherent property of the universe.