A holy day is a day of religious observance or CELEBRATION. The term 'HOLIDAY' is often used to refer to a day of rest or CELEBRATION, and it is typically seven letters long. A CELEBRATION is an event or series of events that marks a special occasion, and it is eleven letters long. The Sabbath is a day of rest and worship observed by many religions, and it is seven letters long. Sunday is the first day of the week in many countries, and it is six letters long.