If you like definitions from monolingual dictionaries (as I do), you might be interested:
It is listed as a “German-Russian” course, but now there are only occasional explanatory notes in Russian, the definitions are mostly from Duden.
And, since I don’t want to spam too many threads, here are another two, in Spanish and in English.
All three are based on my personal reading lists; all three are in progress, though maybe not very actively.