This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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adj. Not to be believed; incredible: unbelievable luck.

adj. Not to be believed.

adj. Incredible; so surprising it is almost unable to believe.

adj. Implausible or improbable.

Not to be believed; incredible.

adj. having a probability too low to inspire belief

adj. beyond belief or understanding

"Outside court, Mr. Boyland expressed relief and thanked his legal team and supporters, repeating the word "unbelievable" three times."

implausible    dumfounding    undreamt of    marvellous    improbable    undreamed    marvelous    undreamed of    astounding    unimagined   

believable   

incredible    disbelievable    inconceivable   

achievable    believable    conceivable    inconceivable    receivable   

incredible    astound    inconceivable    appal    terrify    unheard-of    unprecedented    unbearable    indescribable    unthinkable