The Collaborative International Dictionary of English v.0.48:

Propitious \Pro*pi"tious\, a. [L. propitius, perhaps originally
   a term of augury meaning, flying forward (pro) or well; cf.
   Skr. pat to fly, E. petition, feather.]
   [1913 Webster]
   1. Convenient; auspicious; favorable; kind; as, a propitious
      season; a propitious breeze.
      [1913 Webster]

   2. Hence, kind; gracious; merciful; helpful; -- said of a
      person or a divinity. --Milton.
      [1913 Webster]

            And now t' assuage the force of this new flame,
            And make thee [Love] more propitious in my need.
                                                  --Spenser.
      [1913 Webster]

   Syn: Auspicious; favorable; kind.

   Usage: Propitious, Auspicious. Auspicious (from the
          ancient idea of auspices, or omens) denotes
          "indicative of success," or "favored by incidental
          occurrences;" as, an auspicious opening; an auspicious
          event. Propitious denotes that which efficaciously
          protect us in some undertaking, speeds our exertions,
          and decides our success; as, propitious gales;
          propitious influences.
          [1913 Webster] -- Pro*pi"tious*ly, adv. --
          Pro*pi"tious*ness, n.
          [1913 Webster]

WordNet (r) 3.0 (2006):

propitious
    adj 1: presenting favorable circumstances; likely to result in
           or show signs of success; "propitious omens"; "propitious
           gales speeded us along"; "a propitious alignment of
           planets for space exploration" [ant: unpropitious]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "propitious":
   advantageous, amicable, appropriate, auspicious, befitting,
   beneficent, beneficial, benevolent, benign, benignant, brave,
   bright, bright with promise, cheering, convenient, cooperative,
   dexter, encouraging, expedient, fair, favorable, favoring,
   felicitous, fit, fitting, fortunate, friendly, full of promise,
   golden, good, happy, helpful, inspiring, inspiriting, kind, kindly,
   kindly-disposed, looking up, lucky, meet, neighborly, of good omen,
   of happy portent, of promise, opportune, pregnant of good,
   promising, prosperous, providential, reassuring, ripe, rosy,
   seasonable, sortable, suitable, supportive, timely, toward, useful,
   well-affected, well-disposed, well-intentioned, well-meaning,
   well-meant, well-timed, white