uncertain

adjective

1 the environmental effects of the project are uncertain:

unknown, undetermined, unsettled, unresolved, unsure, pending, in the balance, in limbo, up in the air, debatable, open to question, in doubt;

unpredictable, unforeseeable, incalculable, speculative;

unreliable, untrustworthy, undependable, risky, chancy;

informal dicey, hairy, iffy;

British, informal dodgy.

▷antonyms certain, settled; predictable.

2 the uncertain weather meant that passengers needed to pack a pullover or two:

changeable, variable, varying, irregular, fitful, unpredictable, unreliable, unsettled, unstable, erratic, fluctuating;

informal peaky;

rare changeful, fluctuant.

3 Edward was a little uncertain about the decision:

unsure, doubtful, dubious, undecided, unresolved, indecisive, irresolute, hesitant, wavering, vacillating, oscillating, equivocating, vague, hazy, unclear, ambivalent, in two minds, on the horns of a dilemma, torn;

informal iffy, blowing hot and cold, on the fence.

▷antonyms certain, sure.

4 I gave her an uncertain smile:

hesitant, hesitating, tentative, halting, faltering, unsure, unconfident, diffident, doubtful.

▷antonyms confident.

uncertain Oxford Dictionary of English