'hoodlum' originates from American English (mid 19th century); the exact source is uncertain but it first appeared in San Francisco slang, used to mean a ruffian or gang member.

'hoodlum' was recorded in newspapers and police reports in the 1860s-1870s in San Francisco and then spread into wider U.S. usage; its form has remained largely unchanged since its early slang use.

Initially it referred to specific gang members or rowdy youths in localized slang; over time it has generalized to mean any thug, ruffian, or violent troublemaker.