What is the X in X-mas?
major river of Europe (German Donau, Hungarian Duna, Russian Dunaj), from Latin Danuvius, from Celtic *danu(w)-yo-, from PIE *danu- "river" (cf. Don, Dnieper, Dniester).
River in central and southeastern Europe.
Note: Flowing for nearly two thousand miles, it is the second-longest European river, after the Volga.
Note: Composer Johann Strauss, the Younger, expressed the charm and romance of the river in his “Blue Danube Waltz.”