A tavern, bar or saloon. The term originated in 18th Century England when many drinking establishments made their own gin. The term had a negative connotation at the time. Still in use in English-speaking countries the 21st century
You can find Bobby sitting under the tap in some gin mill.
That's not a night club. It's just a high-priced gin mill.
He tended bar in a little gin mill on the corner of Leonard Street.