From a Germanic name meaning "eagle power", derived from the elements arn "eagle" and wald "power". The Normans brought it to England, where it replaced the Old English cognate Earnweald. It died out as an English name after the Middle Ages, but it was revived in the 19th century.
Saints bearing the name include an 8th-century musician in the court of Charlemagne and an 11th-century French bishop who is the patron saint of brewers. It was also borne by Arnold of Brescia, a 12th-century Augustinian monk who rebelled against the church and was eventually hanged. Famous modern bearers include American golfer Arnold Palmer (1929-2016) and Austrian-American actor and politician Arnold Schwarzenegger (1947-).