I was reminded that Christmas was first celebrated in the 4th century AD but the expression "Merry Christmas" was first used in 1699.
Here's the rest of the story:
The term Merry Christmas is not only used by the Christians to greet each other during the festival of Christmas but by all, irrespective of class as well as religion at the time of the Christmas Festival. In the term Merry Christmas, 'Merry' stands for happiness while 'Christmas' meant Christ's Mass in old English.
To learn more, just Google "origin of 'Merry' Christmas" or go here.