The Deplorable Word, as used in The Magician's Nephew, by author C. S. Lewis, is a magicalcurse which ends all life in the fictional world of Charn except that of the one who speaks it. Lewis does not explicitly link the Deplorable Word to nuclear weapons, but he certainly makes allusions to the power of humanity to destroy itself. Writing in 1955 in the midst of the Cold War, Lewis has the lion Aslan say to the central characters, who are children:
It is not certain that some wicked one of your race will not find out a secret as evil as the Deplorable Word and use it to destroy all living things. And soon, very soon, before you are an old man and an old woman, great nations of your world will be ruled by tyrants who care no more for joy and justice and mercy than the Empress Jadis. Let your world beware. That is the warning.
The children, Digory Kirke and Polly Plummer, come to a lifeless world called Charn. In an ancient, ruined building they awaken a queen, Jadis. She tells them of a worldwide civil war she fought with her sister. All of Jadis' armies were defeated, having been made to fight to the death of the last soldier, and her sister claimed victory. Then Jadis spoke the horrible curse which her sister knew she had discovered but did not think she would use. In speaking the Deplorable Word, Jadis killed every living thing in her world, except herself, to force her sister from the throne. She describes this as "a matter of state".
The children are shocked by this account, but Jadis has no remorse or pity for all the ordinary people whom she killed; in her eyes, they only existed for her to use. The past rulers of her race, who evidently had not always been evil, knew of the Deplorable Word's existence but not the word itself, and had vowed that none of them, nor their descendants, would seek to discover it. Jadis said she had "learned it in a secret place and paid a terrible price to learn it". The book does not say what that price was, or give further details on the Deplorable Word. In The Lion, the Witch, and the Wardrobe, Jadis is rumoured to be a descendant of Lilith, Adam's first wife. Wikipedia's references to Lilith describe how she dared to speak out loud the unspeakable syllables of God's name as a demonstration of her strength and independence and paid a price for this.