Synonyms of the word

unthinkable

• adj. Incapable of being believed; incredible.
• adj. Inconceivable or unimaginable; extremely improbable in a way that goes against common sense.

impossible

• adj. Not possible; not able to be done or happen.
• adj. (colloquial, of a person) Very difficult to deal with.
• adj. (mathematics, dated) imaginary.
• n. (obsolete) an impossibility.

inconceivable

• adj. unable to be conceived, unbelievable.

incredible

• adj. Too implausible to be credible; beyond belief; unbelievable.
• adj. Amazing; astonishing; awe-inspiring.
• adj. Marvellous; profoundly affecting; wonderful.

unbelievable

• adj. Not to be believed.
• adj. Incredible; so surprising it is almost unable to believe.
• adj. Implausible or improbable.

unimaginable

• adj. unable to be imagined; inconceivable or mind-boggling; beyond belief.