fill-mill, n. — Green’s Dictionary of Slang

fill-mill n.

[SE fill + mill, a building characterized by the task performed within it, in this case ‘filling’]

(orig. US black) a bar, a saloon.

1944		D. Burley N.Y. Amsterdam News 15 Jan. 10A: The fill-mills, the gin-dens and the glad-pads.
1946		Mezzrow & Wolfe Really the Blues 147: This fillmill became the hangout for all of Chicago’s hot men.