Source : Webster's Revised Unabridged Dictionary (1913)

Perturbation \Per`tur*ba"tion\, n. [L. perturbatio: cf. F.
   perturbation.]
   1. The act of perturbing, or the state of being perturbed;
      esp., agitation of mind.

   2. (Astron.) A disturbance in the regular elliptic or other
      motion of a heavenly body, produced by some force
      additional to that which causes its regular motion; as,
      the perturbations of the planets are caused by their
      attraction on each other. --Newcomb.

Source : WordNet®

perturbation
     n 1: an unhappy and worried mental state; "there was too much
          anger and disturbance"; "she didn't realize the upset
          she caused me" [syn: {disturbance}, {upset}]
     2: (physics) a secondary influence on a system that causes it
        to deviate slightly
     3: activity that is an intrusion or interruption; "he looked
        around for the source of the disturbance"; "there was a
        disturbance of neural function" [syn: {disturbance}]
     4: a disposition that is confused or nervous and upset [syn: {fluster}]
     5: the act of causing disorder [syn: {disruption}]