Unperson
In the George Orwell book Nineteen Eighty-Four, an 'Unperson' is someone who has been vaporized. Vaporization is when a person is murdered by being turned into vapors. The point of this was that such a person would be gone from all citizens' memories, even friends and family. There is no Newspeak word for what happened to unpeople, therefore it is thoughtcrime to say an unperson's name or think of unpeople.