speakeasy

noun2

1. •
   In modern times, a legal bar in the style of a speakeasy, i.e. one that is hidden away and has a quiet atmosphere.
2. •
   (historical) An illegal saloon or tavern, especially one operated during the American Prohibition period in the 1920s.

   • Many of the legitimate nightclubs of today sprang like legalized phoenixes from the still-hot ashes of the speakeasies of prohibition days. — 1946