cus·tu·mal \ˈkəstəməl, -schəm-\noun orcus·tom·al\-stəm-\ (-s) Etymology: Medieval Latin (liber) custumalis, from Latin liber book + Medieval Latin custumalis of customs, from Old French costumal, from costume custom + -al — more at custom : a written collection of the customs of a monastery, a manor, or a locality