The Collaborative International Dictionary of English v.0.48:

Rundle \Run"dle\, n. [E. round. Cf. Rondle.]
   1. A round; a step of a ladder; a rung. --Duppa.
      [1913 Webster]

   2. A ball. [Obs.] --Holland.
      [1913 Webster]

   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." --Bp. Wilkins.
      [1913 Webster]

   4. (Mach.) One of the pins or trundles of a lantern wheel.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rundle
    n 1: one of the crosspieces that form the steps of a ladder
         [syn: rundle, spoke, rung]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "rundle":
   adolescent stream, arroyo, beck, bourn, braided stream, branch,
   brook, brooklet, burn, carousel, channel, creek, crick, disk,
   doorstep, flowing stream, fluviation, footrest, footstep, fresh,
   freshet, gill, kill, lazy stream, meandering stream,
   merry-go-round, midchannel, midstream, millstream, moving road,
   navigable river, race, racing stream, rest, riser, river, rivulet,
   roller, rolling stone, rotator, rotor, round, roundabout, run,
   rung, runlet, runnel, scale, sike, spill stream, spoke, stair,
   stave, step, step stool, stepping-stone, stream, stream action,
   streamlet, string, subterranean river, top, tread, wadi,
   watercourse, waterway, wheel, whirlabout, whirler, whirligig