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

• Lexulous
• Wordscraper
• Wordosaur

adj. Impossible to imagine; inconceivable: an unthinkable amount of money.

adj. Contrary to what is plausible or probable: That this project would achieve ultimate success was unthinkable at the time.

adj. Not to be thought of or considered; out of the question: Raising taxes was politically unthinkable.

adj. Incapable of being believed; incredible.

adj. Inconceivable or unimaginable; extremely improbable in a way that goes against common sense.

That cannot be made an object of thought; that cannot be thought; incogitable.

adj. incapable of being conceived or considered

"The one option you need to regard as unthinkable is to stay with this person."

out of the question    impossible    inconceivable    unimaginable   

thinkable   

inconceivable    insupposable    incogitable   

unsinkable   

inconceivable    unbelievable    incomprehensible    incalculable    unspeakable    indefensible    inadmissible    untenable    impracticable    unfathomable