fist (n.) Look up fist at Dictionary.com
Old English fyst "fist, clenched hand," from West Germanic *fustiz (cognates: Old Saxon fust, Old High German fust, Old Frisian fest, Middle Dutch vuust, Dutch vuist, German Faust), from Proto-Germanic *funhstiz, probably ultimately from PIE *penkwe- "five" (see five, and compare Old Church Slavonic pesti, Russian piasti "fist").

Meaning "a blow with the fist" is from 1767. Fist-fight "duel with the fists" is from c.1600. As a verb, Old English had fystlian "to strike with the fist."