In Chapter Five of The Magician's Nephew, the Queen explains The Deplorable Word to Digory and Polly: "It had long been known to the great kings of our race that there was a word which, if spoken with the proper ceremonies, would destroy all living things except the one who spoke it."
I didn't realize this the first time I read that part (because The Deplorable Word comes first), but The Deplorable Word is sort of the opposite of what Aslan does in Chapters Eight and Nine. He sings Narnia into existence:
When a line of dark firs sprang up on a ridge about a hundred yards away she [Polly] felt that they were connected with a series of deep, prolonged notes which the Lion had sung a second before. And when he burst into a rapid series of lighter notes she was not surprised to see primroses suddenly appearing in every direction. Thus, with an unspeakable thrill, she felt quite certain that all the things were coming (as she said) "out of the Lion's head". When you listened to his song you heard the things he was making up: when you looked around you, you saw them.Where Aslan's singing brings things into life and existence, the Queen's Deplorable Word "destroy[s] all living things."
