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In the Christian tradition, Sunday is the Sabbath - a day of rest and worship. And as Christianity spread throughout the Roman Empire, the Romans changed the name of the first day of the week to dies dominicus, or day of the Lord. Thus languages that trace their roots to Latin, such as French and Spanish, have different names for Sunday: dimanche in French, domingo in Spanish.
Today Sunday is a day of relaxation in most places - schools and most businesses are closed, and people spend the day as they please. But in the past, observance of the Sabbath was often strictly enforced. The Puritan colonists who settled in New England, for example, had rigid rules: There could be no work and no play. People spent the day at the meeting house, praying and listening to sermons, and even simple activities such as cooking, running, kissing, and cutting hair were banned. (Grolier Book of Knowledge Encyclopedia)