NEW YEAR's is over, so German-speakers are through wishing each other guten Rutsch. “Have a good slide” has a certain surface plausibility to a non-German: you glide into the next year, hoping perhaps that the momentum will carry you through until the following December. (Offered on Berlin's icy pavements, the greeting can sound vaguely unfriendly.) No one is sure where it comes from. Wikipedia offers two possibilities.

Rutsch was a jovial 19th-century way of saying “trip” or “journey”, inspired perhaps by sleds and then by the advent of rail. The Grimm Brothers' dictionary quotes Goethe: “sonntag rutscht man auf das Land,” or “on Sunday we go to the countryside.” The shift from space to time may have happened at the beginning of the 20th century, when "guten Rutsch" shows up as a greeting on newly popular picture postcards.

More intriguing is the possibility that it was imported from Hebrew via Yiddish by way of “Rotwelsch”, the argot of marginal groups like pedlars, beggars and prostitutes. On this theory, guten Rutsch was begotten by Rosh Hashanah, the Jewish new year (literally “head of the year”). “Rosh” meant “head” in Rotwelsch-speaking circles in the middle of the 18th century. Yiddish parentage is the more popular explanation but, sadly, it sounds the less likely. For one thing, Rosh Hashanah falls in September or October, not at the end of the Gregorian year. Jews referred to the Christian version simply as shanah khadashah, “new year” in Hebrew. For another, many Yiddish-speakers say something closer to “rausch” or "roish" than “rosh” and it's a stretch from any of those to “Rutsch”. Which is a pity. Yiddish is basically German leavened with Hebrew, Aramaic and Slavic ingredients. It would be nice to think that more traffic also flowed the other way. German has borrowed chutzpah and other bits from Yiddish, but probably not the cheerful guten Rutsch.