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]