Green’s Dictionary of Slang

(US) an illicit drinking establishment.

1941		J.M. Cain Mildred Pierce (1985) 346: The other way, making a grand tour of all the speako’s he knows, it could go on for five years.
1993		(con. 1920s) I.L. Allen City in Sl. (1995) 72: Most people called them speakeasies [...] A flip speako, affixing a familiar slang device, almost an exclamation of ‘Oh!,’ also appeared.