Oxford Advanced American Dictionary

Definition of unthinkable adjective from the Oxford Advanced Learner's Dictionary

unthinkable

adjective
unthinkable pronunciation English ʌnˈθɪŋkəbl unthinkable pronunciation American ʌnˈθɪŋkəbl
 
unthinkable (for somebody) (to do something)| unthinkable (that…) impossible to imagine or accept
Synonym
inconceivableIt was unthinkable that she could be dead.
Opposite
thinkablethe unthinkable
the unthinkable pronunciation English the unthinkable pronunciation American
noun [singular]Suddenly the unthinkable happened and he drew out a gun.The time has come to think the unthinkable (= consider possibilities that used to be unacceptable).