Meaning of “unthinkable” - Learner’s Dictionary

unthinkable

adjective uk us /ʌnˈθɪŋkəbl/

If something is unthinkable, it is so strange that you cannot imagine it will ever happen:

Thirty years ago a no-smoking restaurant would have been unthinkable.

(Definition of “unthinkable” from the Cambridge Learner’s Dictionary © Cambridge University Press)