From Longman Dictionary of Contemporary Englishthe unthinkablethe unthinkablesomething that is impossible to accept or imagine Then the unthinkable happened and the boat started to sink. It was the job of the committee to think the unthinkable (=plan for unexpected events or situations). → unthinkable
Examples from the Corpus
think the unthinkable• Aided by sufficient alcohol, we might all be prepared to start thinking the unthinkable.• But gradually Mr Fox and his allies persuaded voters to think the unthinkable.• He is qualified to think the unthinkable and to pose those questions which in normal circumstances would go unasked.• Once vice-chancellors start to think the unthinkable, then the issue becomes part of the agenda and it becomes harder to retreat. 