Definition of "speakeasy"

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

1946, George Johnston, Skyscrapers in the Mist, page 90

Retuning[sic] to Gotham, he came to intimately know Manhattan's speakeasy scene. “At a speakeasy,” Hirschfeld acknowledged, “you had to be known to get in...each place had its own clientele.” Membership cards, really fake IDs, were common.

2020, David Rosen, Prohibition New York City, Arcadia Publishing, page 39