run·dle /ˈrʌndḷ/
  梯級
  Run·dle n.
  1. A round; a step of a ladder; a rung.
  2. A ball. [Obs.]
  3. Something which rotates about an axis, as a wheel, or the drum of a capstan. “An axis or cylinder having a rundle about it.”
  4. Mach. One of the pins or trundles of a lantern wheel.
  ◄ ►
  rundle
       n : one of the crosspieces that form the steps of a ladder [syn:
            spoke, rung]