“Monday is the day of the week between Sunday and Tuesday. According to the traditional Christian, Islamic and Hebrew calendars, it is the second day of the week, and according to international standard ISO 8601 it is the first day of the week. In the West, it is the first day of the work week, whereas in most Muslim countries and Israel, it is the second day of the work week. The name of Monday is derived from Old English Mōnandæg and Middle English Monenday, which means “moon day”.
Definition doesn’t fit right…..
Here, let me try a picture instead.