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.
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   2. To vary or fluctuate between fixed limits; to act or move
      in a fickle or fluctuating manner; to change repeatedly,
      back and forth.
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            The amount of superior families oscillates rather
            than changes, that is, it fluctuates within fixed
            limits.                               --De Quincey.
      [1913 Webster]