River in a Strauss waltz's title (6)

I believe the answer is:

danube

(Other definitions for danube that I've seen before include "Great European river, musically blue (6)" , "Major European river" , "River in Europe" , "Central European river" , "Viennese river" .)

I've seen this clue in the Universal.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.