Merry Christmas 實際上起源於英國壹個名字叫John Calcott Horsely 的人。英國人當年在19世紀初的時候互送賀卡的時候，都是人工做的卡片，上面寫上祝福的話的。 可是當年Horsely 則是第壹個批量印刷Christmas card 的人， 而他本人就是寫的Merry Christmas 的， 以後人們都如法炮制，沿用至今。
1、merry 以有趣和快樂為特征的或令人感到有趣和快樂的；歡樂的。
如：a merry joke 逗樂的笑話?
2、happy 指愉快的，快樂的：享受、顯示或表現出快樂、滿足或歡樂的。
happy有時表示“快樂”的升級：幸福。
happy life：幸福生活。
兩種說法沒區別，談不上哪個是固定短語 ，但Merry Christmas 比較地道。
擴展資料：
聖誕節的來歷：
Christmas is of course a religious festival. It’s all about celebrating the birth of Jesus Christ.?
聖誕節無疑是壹個宗教節日。它是為了慶祝耶穌的誕生。
In fact, there’s no mention of December 25th in the Bible. Early Christians couldn’t even agree on which day Jesus was actually born. It was only in the 3rd century that December 25th became the official celebration of the birth of Jesus. Most likely because it coincided with already existing Pagan festivals.?
其實，聖經上是並沒有提到過12月25號這個日子的。早年的基督教徒們也壹直對基督具體出生的日子爭論不休最終也沒有個確切的結果。壹直到公元3世紀，才把12月25日定為官方的慶祝耶穌誕生的日子。很可能是和當時已經存在的壹些異教徒節的日期有關。
A Christmas tree can be found in most British homes throughout the month of December. In the earliest history of Scandinavia, it was traditional during the celebration of the Winter Solstice (December 21st) to bring an evergreen tree into the home and decorate it. Since the evergreen was the only type of tree that lived through the entire winter, the families saw it as a symbol of continued life.?
大部分英國的家庭都會在12月份在家放壹棵聖誕樹。最初起源於斯堪的納維亞，那裏的人為了慶祝冬至，會帶壹棵常青樹回家並且裝飾它。因為常青樹是唯壹壹種能存活過壹整個冬季的樹，所以他們把它看成是生命延續的象征。