late 14c., riotour, "debauchee, one who leads a dissolute life, roisterer," from Old French riotour, from riote "dispute, quarrel, domestic strife" (see riot (n.)). The ending was altered late 16c. to conform to -er (1). Meaning "one who takes part in a rising or public disturbance against authority" is from mid-15c. (from late 14c. in Anglo-French).