The story
From Humpty Dumpty + -ism, after the fictional character in Lewis Carroll's Through the Looking-Glass, who, when asked what he means by glory, replies, "I meant 'there's a nice knock-down argument for you!'" Alice protests that this isn't the meaning of glory and Humpty Dumpty replies, "When I use a word, it means just what I choose it to mean——neither more nor less."
Etymology from Wiktionary, CC BY-SA 4.0.