The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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, perturbation, upset]
    2: (physics) a secondary influence on a system that causes it to
       deviate slightly
    3: activity that is a malfunction, intrusion, or interruption;
       "the term `distress' connotes some degree of perturbation and
       emotional upset"; "he looked around for the source of the
       disturbance"; "there was a disturbance of neural function"
       [syn: perturbation, disturbance]
    4: a disposition that is confused or nervous and upset [syn:
       perturbation, fluster]
    5: the act of causing disorder [syn: disruption,
       perturbation]

Moby Thesaurus II by Grady Ward, 1.0:

235 Moby Thesaurus words for "perturbation":
   ado, aggravation, agitation, all-overs, angst, animation, anxiety,
   anxiety hysteria, anxiety neurosis, anxious bench, anxious concern,
   anxious seat, anxiousness, apprehension, apprehensiveness, arousal,
   arousing, baffle, bafflement, befuddlement, bewilderment, bluster,
   bobbery, boil, boiling, bother, botheration, brouhaha, bustle,
   cankerworm of care, care, chaos, chills of fear, churn, cloud,
   cold creeps, cold shivers, cold sweat, commotion, concern,
   concernment, confoundment, confusion, conturbation, convulsion,
   creeps, daze, derangement, dilemma, disarrangement, disarray,
   disarticulation, discombobulation, discomfiture, discomposure,
   disconcert, disconcertedness, disconcertion, disconcertment,
   disharmony, dishevelment, disintegration, disjunction, dislocation,
   disorder, disorderliness, disorganization, disorientation,
   disproportion, disquiet, disquietude, disruption, distress,
   disturbance, dread, ebullience, ebullition, eddy, effervescence,
   electrification, embarrassment, embroilment, enigma, entropy,
   exacerbation, exasperation, excitation, excitement, exhilaration,
   fear, fear and trembling, feery-fary, ferment, fermentation, fever,
   feverishness, fidgets, fix, flap, flummox, flurry, fluster,
   flutter, flutteration, fog, foment, fomentation, foreboding,
   forebodingness, frenzy, fuddle, fuddlement, fume, fuss,
   galvanization, goose bumps, gooseflesh, haphazardness, haze,
   heartquake, horripilation, hubbub, hurly-burly, hurry,
   hurry-scurry, incitement, incoherence, indiscriminateness,
   inflammation, infuriation, inharmonious harmony, inquietude,
   insanity, irregularity, irritation, jam, jimjams, jitters, jumble,
   jumpiness, lathering up, maelstrom, malaise, maze, mess,
   misarrangement, misgiving, mist, moil, most admired disorder,
   muddle, muddlement, mystery, nerviness, nervous tension,
   nervousness, nonplus, nonsymmetry, nonuniformity, overanxiety,
   palpitation, pell-mell, perplexity, pickle, pins and needles,
   plight, pother, predicament, problem, promiscuity, promiscuousness,
   provocation, pucker, puzzle, puzzlement, quaking, quandary,
   quiver of terror, randomness, restlessness, riddle, roil, rout,
   row, ruffle, scrape, seethe, seething, shivers, shuffle, shuffling,
   solicitude, steaming up, stew, stimulation, stimulus, stir,
   stirring, stirring up, strain, suspense, sweat, swirl, swirling,
   swivet, tension, thrill of fear, tizzy, to-do, trepidation,
   trepidity, trouble, tumult, tumultuation, turbidity, turbulence,
   turmoil, twitter, unassuredness, unease, uneasiness, unquietness,
   unrest, unsettlement, unsymmetry, ununiformity, uproar, upset,
   vexation, vortex, whipping up, whirl, working up, yeastiness,
   zeal



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PERTURBATION. This is a technical word which signifies disturbance, or
infringement of a right. It is usually applied to the disturbance of pews,
or seats in a church. In the ecclesiastical courts actions for these
disturbances are technically called "suits for perturbation of seat." 1
Phillim. 323. Vide Pew.