tavern vs rathskeller

tavern and rathskeller both are nouns.

Word	Noun	Adjective	Verb	Adverb
tavern	Yes	No	No	No
rathskeller	Yes	No	No	No

As nouns, rathskeller is a hyponym of tavern; that is, rathskeller is a word with a more specific, narrower meaning than tavern:

tavern: a building with a bar that is licensed to sell alcoholic drinks
rathskeller: a tavern below street level featuring beer; originally a German restaurant in the basement of city hall

Other hyponyms of tavern include beer garden, bucket shop, gin mill, pothouse, pub, public house, saloon, taphouse, shebeen.

tavern (noun)	rathskeller (noun)
a building with a bar that is licensed to sell alcoholic drinks	a tavern below street level featuring beer; originally a German restaurant in the basement of city hall