Source : Webster's Revised Unabridged Dictionary (1913)

Rathskeller \Raths"kel`ler\ (r[aum]ts"k[e^]l*l[~e]r), n. [G.,
   also {ratskeller}, prop., town-hall cellar.]
   Orig., in Germany, the cellar or basement of the city hall,
   usually rented for use as a restaurant where beer is sold;
   hence, a beer saloon of the German type below the street
   level, where, usually, drinks are served only at tables and
   simple food may also be had; -- sometimes loosely used, in
   English, of what are essentially basement restaurants where
   liquors are served.

Source : WordNet®

rathskeller
     n : a tavern below street level featuring beer; originally a
         German restaurant in the basement of city hall