You can say happy christmas. This sentence itself is correct and correct. It is just a matter of habit.

People are accustomed to saying Merry Christmas merry, which means wishing and praying. Christmas is very sacred to the West. It is the birthday of Jesus Christ. It can be said that merry Christmas has become their first consciousness.

There is absolutely nothing wrong with the meaning and usage of Happy Christmas, but they have formed a fixed combination of "Merry Christmas" over hundreds of years of history. Santa Claus is a Santa Claus who secretly delivers gifts to children on Christmas Eve. It can also be called Father Christmas or Santa.

The meaning of merry in English

The meaning of the word merry in English has always been pleasant (pleasant), but in 1843 Dickens's "A Christmas Carol" (A Christmas Carol) , giving merry the meaning of "being tipsy (from drinking)".

For example, there is a famous saying in English: Eat, drink and be merry, for tomorrow we die. The meaning of this sentence is "Eat, drink and be merry, for tomorrow we will die." In fact, It means "life is short, take pleasure in the moment".