来自古英语 hrung,横杆,挡板。后用于指梯子的横档,梯级。
This [rungs] has generally been considered as a mere corruption of rounds; and people of education use only this latter word. [John Pickering, "A Vocabulary or Collection of Words and Phrases which have been Supposed to be Peculiar to the United States of America," Boston, 1816]