The Collaborative International Dictionary of English v.0.48:

Prosperous \Pros"per*ous\, a. [L. prosperus or prosper,
   originally, answering to hope; pro according to + the root of
   sperare to hope. See Despair.]
   1. Tending to prosperity; favoring; favorable; helpful.
      [1913 Webster]

            A happy passage and a prosperous wind. --Denham.
      [1913 Webster]

   2. Being prospered; advancing in the pursuit of anything
      desirable; making gain, or increase; thriving; successful;
      as, a prosperous voyage; a prosperous undertaking; a
      prosperous man or nation.
      [1913 Webster]

            By moderation either state to bear
            Prosperous or adverse.                --Milton.
      [1913 Webster]

   Syn: Fortunate; successful; flourishing; thriving; favorable;
        auspicious; lucky. See Fortunate.
        [1913 Webster] -- Pros"per*ous*ly, adv. --
        Pros"per*ous*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

prosperous
    adj 1: in fortunate circumstances financially; moderately rich;
           "they were comfortable or even wealthy by some
           standards"; "easy living"; "a prosperous family"; "his
           family is well-situated financially"; "well-to-do members
           of the community" [syn: comfortable, easy,
           prosperous, well-fixed, well-heeled, well-off,
           well-situated, well-to-do]
    2: very lively and profitable; "flourishing businesses"; "a
       palmy time for stockbrokers"; "a prosperous new business";
       "doing a roaring trade"; "a thriving tourist center"; "did a
       thriving business in orchids" [syn: booming, flourishing,
       palmy, prospering, prosperous, roaring, thriving]
    3: marked by peace and prosperity; "a golden era"; "the halcyon
       days of the clipper trade" [syn: golden, halcyon,
       prosperous]
    4: presaging or likely to bring good luck; "a favorable time to
       ask for a raise"; "lucky stars"; "a prosperous moment to make
       a decision" [syn: golden, favorable, favourable,
       lucky, prosperous]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "prosperous":
   abounding in riches, affluent, appropriate, assured of success,
   auspicious, benign, benignant, booming, comfortable,
   comfortably situated, coming, convenient, crowned with success,
   desirable, disgustingly rich, easy, fair, fat, favorable, favoring,
   felicitous, flourishing, flush, fortunate, frightfully rich,
   full of promise, golden, good, halcyon, happy, in clover, in funds,
   in good case, in luxury, in the money, independent,
   independently rich, independently wealthy, loaded, lucky,
   luxurious, made, made of money, moneyed, monied, of good omen,
   of happy portent, of promise, on Easy Street, on the up-and-up,
   on top, on velvet, oofy, opportune, opulent, out in front,
   promising, propitious, prospering, provided for, rich,
   rich as Croesus, rolling in money, seasonable, snug, strong,
   substantial, succeeding, successful, surefire, thriving,
   triumphant, wallowing in wealth, warm, wealthy, well,
   well provided for, well-fixed, well-heeled, well-off, well-timed,
   well-to-do