The Collaborative International Dictionary of English v.0.48:

Oscillation \Os`cil*la"tion\, n. [L. oscillatio a swinging.]
   [1913 Webster]
   1. The act of oscillating; a swinging or moving backward and
      forward, like a pendulum; vibration.
      [1913 Webster]

   2. Fluctuation; variation; change back and forth.
      [1913 Webster]

            His mind oscillated, undoubtedly; but the extreme
            points of the oscillation were not very remote.
                                                  --Macaulay.
      [1913 Webster]

   Axis of oscillation, Center of oscillation. See under
      Axis, and Center.
      [1913 Webster]

WordNet (r) 3.0 (2006):

oscillation
    n 1: the process of oscillating between states
    2: (physics) a regular periodic variation in value about a mean
       [syn: oscillation, vibration]
    3: a single complete execution of a periodically repeated
       phenomenon; "a year constitutes a cycle of the seasons" [syn:
       cycle, oscillation]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "oscillation":
   alternation, beat, cyclicalness, equivocation, fluctuation,
   intermittence, intermittency, meter, pendulation, pendulum motion,
   periodicalness, periodicity, piston motion, pulsation,
   reappearance, recurrence, regular wave motion, reoccurrence,
   return, rhythm, seasonality, seesawing, shifting, shilly-shally,
   shilly-shallying, shuffling, teeter-tottering, teetering,
   tottering, undulation, vacillation, variation, vicissitude,
   wavering, wobbling