Monday/ˈmʌndeɪ/ Definition 1 of 2Pro Tip 1/3Order in Week Understand that Monday is often seen as the first day in a new week. The calendar week starts on Monday. Pro Tip 2/3Work Beginnings Many people start their work or school week on Monday. Our office is busiest on Mondays. Pro Tip 3/3Scheduling Reminder Remember, in English-speaking regions, many businesses reopen on Monday. The store is closed on Sundays and reopens on Mondays.