The Collaborative International Dictionary of English v.0.48:

Exorbitant \Ex*or"bi*tant\, a. [L. exorbitans, -antis, p. pr. of
   exorbitare to go out of the track; ex out + orbita track: cf.
   F. exorbitant. See Orbit.]
   1. Departing from an orbit or usual track; hence, deviating
      from the usual or due course; going beyond the appointed
      rules or established limits of right or propriety;
      excessive; extravagant; enormous; inordinate; as,
      exorbitant appetites and passions; exorbitant charges,
      demands, or claims.
      [1913 Webster]

            Foul exorbitant desires.              --Milton.
      [1913 Webster]

   2. Not comprehended in a settled rule or method; anomalous.
      [1913 Webster]

            The Jews . . . [were] inured with causes exorbitant,
            and such as their laws had not provided for.
                                                  --Hooker.
      [1913 Webster]

WordNet (r) 3.0 (2006):

exorbitant
    adj 1: greatly exceeding bounds of reason or moderation;
           "exorbitant rent"; "extortionate prices"; "spends an
           outrageous amount on entertainment"; "usurious interest
           rate"; "unconscionable spending" [syn: exorbitant,
           extortionate, outrageous, steep, unconscionable,
           usurious]