rung (n.) Look up rung at Dictionary.com
Old English hrung "rod, bar," from Proto-Germanic *khrungo (cf. Middle Low German runge, Old High German runga "stake, stud, stave," Middle Dutch ronghe, Dutch rong "rung," Gothic hrugga "staff"), of unknown origin with no connections outside Germanic. Sense in English narrowed to "round or stave of a ladder" (first attested late 13c.), but usage of cognate words remains more general in other Germanic languages.