The Collaborative International Dictionary of English v.0.48:

Righteous \Right"eous\, a. [OE. rightways, rightwise, AS.
   rightw[imac]s; riht right + w[imac]s wise, having wisdom,
   prudent. See Right, a., Wise, a.]
   Doing, or according with, that which is right; yielding to
   all their due; just; equitable; especially, free from wrong,
   guilt, or sin; holy; as, a righteous man or act; a righteous
   retribution.
   [1913 Webster]

         Fearless in his righteous cause.         --Milton.
   [1913 Webster]

   Syn: Upright; just; godly; holy; uncorrupt; virtuous; honest;
        equitable; rightful.
        [1913 Webster]

WordNet (r) 3.0 (2006):

righteous
    adj 1: characterized by or proceeding from accepted standards of
           morality or justice; "the...prayer of a righteous man
           availeth much"- James 5:16 [ant: unrighteous]
    2: morally justified; "righteous indignation"

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "righteous":
   Christendom, Christian, Christlike, Christly, God-fearing,
   according to Hoyle, angelic, appropriate, apt, blameless, clean,
   condign, correct, creditable, decent, decorous, due, erect,
   estimable, ethical, exemplary, fair, fit, fitting,
   full of integrity, godlike, godly, godly-minded, good, guiltless,
   heavenly, high-minded, high-principled, highly respectable, holy,
   holy-minded, honest, honorable, immaculate, inculpable, innocent,
   inviolate, irreproachable, just, justifiable, justified, kosher,
   law-abiding, law-loving, law-revering, manly, moral, moralistic,
   nice, noble, normal, normative, otherworldly, principled, proper,
   pure, pure in heart, purehearted, reputable, respectable, right,
   right and proper, right-minded, rightful, saintlike, saintly,
   seemly, self-righteous, seraphic, spiritual, spiritual-minded,
   spotless, stainless, sterling, straight, suitable, the believing,
   the chosen, the elect, the faithful, the good, the righteous,
   the saved, true-dealing, true-devoted, true-disposing, true-souled,
   true-spirited, truehearted, trustworthy, unblamable, unblemished,
   uncorrupt, uncorrupted, undefiled, unearthly, unimpeachable,
   unspotted, unstained, unsullied, untarnished, unworldly, upright,
   uprighteous, upstanding, virtuous, worthy, yeomanly