The story
From revenue + -er, reflecting the U.S. Treasury Department's former Bureau of Internal Revenue (a predecessor of the IRS and ATF), because the administrative mechanism for enforcing Prohibition originated in excise tax administration; Wikipedia gives details at Bureau of Alcohol, Tobacco, Firearms and Explosives § History.
First known use, by meaning
- from 19th c. A government official who enforces laws prohibiting the illegal distillation of alcohol.
Etymology from Wiktionary, CC BY-SA 4.0.