This conceptual structural contribution introduces Definition Through Difference as a structure-first account of how identity becomes recognizable. It proposes that definition does not begin with language alone, but with structured difference: a thing becomes definable when it can be distinguished from what it is not, while remaining coherent enough to be recognized as itself. The paper develops the sequence Difference → Distinction → Boundary → Recognition → Definition, arguing that definition appears between two failures: indistinguishability caused by too little difference, and fragmentation caused by too much unstructured difference.