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