Liable to happen or not; of uncertain occurrence or incidence.

Occurring or coming at uncertain times; not to be calculated on, uncertain, unsettled.

Subject to uncertainty or the ‘caprice of fortune’. Obsolete.

Dependent on chance or circumstance; uncertain; liable to fail; exposed to risk, hazardous; insecure, unstable.

Not reliable; inconsistent. Obsolete.

That cannot be calculated. That cannot be reckoned or determined beforehand; incapable of being estimated or forecast.

(un-, prefix1 affix 1b.)

Liable to chance or sudden change, uncertain, ‘casual’, risky, untrustworthy. colloquial or dialect.

That cannot be predicated. (In quot. 1864 loosely = that cannot be predicted.)

Uncertain; favouring unexpected results.

Dependent on uncertain contingencies; left to or resulting from a chance process; aleatory.

attributive (occasionally in plural).

Of a question, proposal, prospect, etc.: full of ‘ifs’, contingent, doubtful.