The first day of the week is Sunday. For most Christian denominations this day is considered a holy day, due to the fact that Christ was reported to have risen from the dead on a Sunday. For this reason, since ancient times, it has been designated a "day of rest" mainly for the purpose of contemplation and worship. (The actual last day of the week when God rested after creating the universe was Saturday.)
Yet the name of Sunday has nothing to do with Christianity, but everything to do with even more ancient religions. The ancient Greeks knew that the sun was the source of life on the planet and they gave it prime importance in their thinking. When the Romans later adopted the seven day week they emphasize their respect for the sun by naming the first day of the week for it..."dies solis"..."day of the sun".
The actual word "Sunday" is derived from the German word "Sonntag" (and they likely got it from the Scandanavians). These folk too placed a great deal of importance on the sun. Some tribes of these Germanic peoples invaded England in the 500's or so. They were known as the Angles and the Saxons. The old English work was "sunnandaeg" and it changed over time to become our current, "Sunday".
There are several holidays that are traditionally held on Sunday. Mother's Day (second Sunday in May) and Father's Day (third Sunday in June) began to be celebrated rather recently, 1914 and 1924 respectively. Easter is an ancient holiday that was officially designated by the Church in the year 325. Its position on the calendar has confused lay people for centuries. The date of Easter is calculated by taking the first Sunday after the first full moon on or after the 21st of March.
Weekdays | Monday