Many disagreements in philosophy, and some in ordinary life, are about issues that it is natural to think of as matters of definition. (Can there be same-sex marriage? Is free will compatible with determinism? Is so-called “conceptual art” really art?) Philosophical accounts of definition distinguish nominal definitions (which either stipulatively introduce a new meaning for a word, or describe an extant meaning) and real definitions (which give an account of the essence of a thing). I argue that ordinary and philosophical disputes about definition do not fit neatly into either of these categories and propose an alternative account.