The Collaborative International Dictionary of English v.0.48:

Oscillating \Os"cil*la`ting\ ([o^]s"s[i^]l*l[=a]`t[i^]ng), a.
   That oscillates; vibrating; swinging.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Oscillate \Os"cil*late\ ([o^]s"s[i^]l*l[=a]t), v. i. [imp. & p.
   p. Oscillated ([o^]s"s[i^]l*l[=a]`t[e^]d); p. pr. & vb. n.
   Oscillating ([o^]s"s[i^]l*l[=a]`t[i^]ng).] [L. oscillare to
   swing, fr. oscillum a swing, a little mask or puppet made to
   be hung from trees and swing in the wind, prob. orig., a
   little mouth, a dim. from os mouth. See Oral, and cf.
   Osculate.]
   [1913 Webster]
   1. To move backward and forward; to vibrate like a pendulum;
      to swing; to sway.
      [1913 Webster]

   2. To vary or fluctuate between fixed limits; to act or move
      in a fickle or fluctuating manner; to change repeatedly,
      back and forth.
      [1913 Webster]

            The amount of superior families oscillates rather
            than changes, that is, it fluctuates within fixed
            limits.                               --De Quincey.
      [1913 Webster]

WordNet (r) 3.0 (2006):

oscillating
    adj 1: having periodic vibrations [syn: oscillatory,
           oscillating]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "oscillating":
   fluctuant, fluctuating, fluctuational, harmonic, libratory,
   nutational, oscillatory, pendular, pendulating, pendulous,
   periodic, resonant, shilly-shally, shilly-shallying, vacillating,
   vacillatory, vibratile, vibrating, vibratory, wavering, wobbly