1. impossible to imagine or consider; too unlikely or shocking to be believed

Examples

• It was unthinkable that she would miss her own wedding.
• The idea of quitting his job seemed unthinkable to him.
• War between the two countries was once unthinkable.
• The cost of the project made it unthinkable for the small company.
• It’s unthinkable that anyone would harm innocent children.
• Twenty years ago, smartphones were unthinkable.
• The unthinkable happened when the champion lost in the first round.