Stephen Goranson has provided verifiable evidence from 1884: an antedating of two years.
A gangster is somebody who is part of a criminal gang. Such gangs have existed for a very long time, but this word for an individual member is a relatively recent development, seemingly originating in the United States in the late 19th century.
The currently published OED entry for gangster has its earliest quotation from 1896; however, in the course of revising the entry, OED editors have already found evidence from a decade earlier, in 1886. This earlier use comes from a Chicago newspaper, which is perhaps unsurprising given that city’s historical association with organized crime:
1886 Chicago Tribune 31 Mar. 3/4 (headline) Aldermanic gangsters—half a dozen bad eggs.
However, this quotation probably represents the Tribune using a colloquial term that had been in use for some time before they printed it. Can you help us find earlier uses of gangster?
Posted by OED_Editor on 7 January 2013 9.25