1. A calendar or schedule, especially one showing the order of religious services or liturgical observances in the Christian church.
Usage: ecclesiastical; formal
2. A prescribed order or sequence; an arrangement or system.
Usage: formal; archaic

Examples

• The priest consulted the ordo to determine which prayers to recite during the service.
• The monastery maintained a strict ordo for daily prayers and meals.
• According to the ordo, the feast day would be celebrated on the third Sunday of the month.
• The ordo outlined the proper sequence of liturgical readings for the entire year.