When you departmentalize a company, a school, or a piece of work, you split it into departments — groups that each look after one kind of job. Sales in one place, money in another, people in another: that is departmentalizing. It is a formal, office word. You hear it in business and in large organizations, not at the dinner table. Though actually, people sometimes use it with a little complaint: if a place is too departmentalized, each team only sees its own work and nobody holds the whole problem. You departmentalize an organization or a system; you do not departmentalize a sandwich.