History of the phrase
"Merry", derived from the Old English myrige, originally meant merely "pleasant" rather than joyous or jolly (as in the phrase "merry month of May").
Though Christmas has been celebrated since the 4th century AD, the first known usage of any Christmastime greeting, "Merry Christmas and a Happy New Year" (thus incorporating two greetings) was in an informal letter written by an English admiral in 1699. The same phrase appeared in the first Christmas card, produced in England in 1843, and in the popular secular carol "We Wish You a Merry Christmas."
The then relatively new term "Merry Christmas" figured prominently in Charles Dickens' A Christmas Carol in 1843. The cynical Ebenezer Scrooge rudely deflects the friendly greeting and broods on the foolishness of those who utter it. "If I could work my will", says Scrooge, "every idiot who goes about with 'Merry Christmas' on his lips, should be boiled with his own pudding." After the Spirits of Christmas effect his transformation, he is able to heartily exchange the wish with all he meets. The continued popularity of A Christmas Carol and the Victorian era Christmas traditions it typifies have led some to credit Dickens with popularizing, or even originating, the phrase "Merry Christmas".
The alternative "Happy Christmas" gained wide usage in the late 19th century, and is still common in the United Kingdom and Ireland. One reason may be the alternative meaning, still current there, of "merry" as "tipsy" or "drunk". Queen Elizabeth II is said to prefer "Happy Christmas" for this reason. In American poet Clement Moore's "A Visit from St. Nicholas" (1823), the final line, originally written as "Happy Christmas to all, and to all a good night", has been changed in many editions to "Merry Christmas to all", perhaps indicating the relative popularity of the phrases in the United States.