The Collaborative International Dictionary of English v.0.48:

Disturb \Dis*turb"\, v. t. [imp. & p. p. Disturbed; p. pr. &
   vb. n. Disturbing.] [OE. desturben, destourben, OF.
   destorber, desturber, destourber, fr. L. disturbare,
   disturbatum; dis- + turbare to disturb, trouble, turba
   disorder, tumult, crowd. See Turbid.]
   1. To throw into disorder or confusion; to derange; to
      interrupt the settled state of; to excite from a state of
      rest.
      [1913 Webster]

            Preparing to disturb
            With all-cofounding war the realms above. --Cowper.
      [1913 Webster]

            The bellow's noise disturbed his quiet rest.
                                                  --Spenser.
      [1913 Webster]

            The utmost which the discontented colonies could do,
            was to disturb authority.             --Burke.
      [1913 Webster]

   2. To agitate the mind of; to deprive of tranquillity; to
      disquiet; to render uneasy; as, a person is disturbed by
      receiving an insult, or his mind is disturbed by envy.
      [1913 Webster]

   3. To turn from a regular or designed course. [Obs.]
      [1913 Webster]

            And disturb
            His inmost counsels from their destined aim.
                                                  --Milton.

   Syn: To disorder; disquiet; agitate; discompose; molest;
        perplex; trouble; incommode; ruffle.
        [1913 Webster]

WordNet (r) 3.0 (2006):

disturbing
    adj 1: causing distress or worry or anxiety; "distressing (or
           disturbing) news"; "lived in heroic if something
           distressful isolation"; "a disturbing amount of crime";
           "a revelation that was most perturbing"; "a new and
           troubling thought"; "in a particularly worrisome
           predicament"; "a worrying situation"; "a worrying time"
           [syn: distressing, distressful, disturbing,
           perturbing, troubling, worrisome, worrying]

Moby Thesaurus II by Grady Ward, 1.0:

100 Moby Thesaurus words for "disturbing":
   aggravating, agitating, alarming, annoying, awkward, baffling,
   bewildering, bothering, bothersome, breathtaking, chafing, charged,
   cliff-hanging, confounding, confusing, crushing, discomposing,
   disconcerting, dismaying, disquieting, distracting, distressful,
   distressing, electric, embarrassing, enigmatic, exasperating,
   exciting, exhilarating, fretting, galling, galvanic, harassing,
   heady, heart-expanding, heart-stirring, heart-swelling,
   heart-thrilling, humiliating, importunate, importune, impressive,
   inflammatory, intoxicating, intricate, irking, irksome, irritating,
   jarring, jolting, maddening, mind-blowing, mortifying, moving,
   mysterious, mystifying, overcoming, overmastering, overpowering,
   overwhelming, perplexing, perturbing, pesky, pestering,
   pestiferous, pestilent, pestilential, piquant, plaguesome, plaguey,
   plaguing, problematic, provocative, provoking, puzzling, ravishing,
   soul-stirring, spirit-stirring, stimulating, stimulative, stirring,
   striking, suspenseful, suspensive, tantalizing, teasing, telling,
   thrilling, thrilly, tiresome, tormenting, troublesome, troubling,
   unsettling, upsetting, vexatious, vexing, wearisome, worrisome,
   worrying