To itemize is to make a list and give the detail for each thing on it, one by one. A shop may itemize a bill so you see milk, bread, and fruit as separate lines, not just one lump called “food.” Offices itemize costs. In American tax talk, to itemize is to list real expenses instead of taking one simple ready-made number — a rather official use. The word feels more businesslike than plain “list.” In British spelling you may see itemise. People sometimes stretch it to mean “spell out every little thing in speech,” as if talking could be a receipt — though actually the core picture is still a list with parts.