1. in a way that is impossible to imagine or consider; to an extreme degree that defies belief

Examples

• The mountain peak was unthinkably high, disappearing into the clouds.
• It would be unthinkably cruel to abandon the injured animal.
• The ancient castle was unthinkably old, dating back over a thousand years.
• The cost of the luxury yacht was unthinkably expensive for most people.
• The desert stretched unthinkably far in every direction.
• It seemed unthinkably difficult to climb the sheer cliff face.