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.
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rundle
n : one of the crosspieces that form the steps of a ladder [syn:
spoke, rung]