The Newspeak word which means the ability to hold two mutually contradictory ideas in mind simultaneously and to believe both of them is

Doublethink is the correct answer because it accurately describes the ability to hold two contradictory ideas simultaneously and believe in both of them. This concept was introduced in George Orwell's novel "1984" and is a central theme in the book. Doublethink represents the state of cognitive dissonance and the manipulation of reality by the totalitarian regime in the novel. It reflects the ability to accept contradictory information without questioning or challenging it, which is a crucial tool for maintaining control over the population.