28 synonyms for unlikely such as cock and bull, absurd, and beyond belief. Unlikely is an adjective, and its antonyms are likely, certain, and believable.
Absurd, beyond belief, cock and bull, doubtful, dubious, fabulous, fanciful, fantastic, far-fetched, hard to swallow/take, implausible, improbable, inconceivable, incredible, laboured, not likely, preposterous, questionable, remote, ridiculous, strained, tall, unbelievable, unconvincing, unexpected, unimaginable, and unrealistic.