The Collaborative International Dictionary of English v.0.48:

Riotous \Ri"ot*ous\, a. [OF. rioteux.]
   1. Involving, or engaging in, riot; wanton; unrestrained;
      luxurious.
      [1913 Webster]

            The younger son . . . took his journey into a far
            country, and there wasted his substance with riotous
            living.                               --Luke xv. 13.
      [1913 Webster]

   2. Partaking of the nature of an unlawful assembly or its
      acts; seditious.
      [1913 Webster] -- Ri"ot*ous*ly, adv. --
      Ri"ot*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

riotous
    adj 1: produced or growing in extreme abundance; "their riotous
           blooming" [syn: exuberant, lush, luxuriant,
           profuse, riotous]
    2: characterized by unrest or disorder or insubordination;
       "effects of the struggle will be violent and disruptive";
       "riotous times"; "these troubled areas"; "the tumultuous
       years of his administration"; "a turbulent and unruly
       childhood" [syn: disruptive, riotous, troubled,
       tumultuous, turbulent]
    3: unrestrained by convention or morality; "Congreve draws a
       debauched aristocratic society"; "deplorably dissipated and
       degraded"; "riotous living"; "fast women" [syn: debauched,
       degenerate, degraded, dissipated, dissolute,
       libertine, profligate, riotous, fast]

Moby Thesaurus II by Grady Ward, 1.0:

173 Moby Thesaurus words for "riotous":
   abandoned, abounding, abundant, affluent, all-sufficing, ample,
   aplenty, boisterous, bottomless, bounteous, bountiful, brawling,
   breakaway, chaotic, copious, debauched, dense, diffuse, disordered,
   disorderly, dissipated, dissolute, effuse, epidemic, exhaustless,
   extravagant, extreme, extremistic, exuberant, factious, fat,
   fertile, flourishing, flush, free-living, full, galore, generous,
   go-go, gross, heavy, high-living, immoderate, impenetrable,
   in plenty, in quantity, incontinent, indulgent, inexhaustible,
   insurgent, insurrectionary, intemperate, irrepressible, jungled,
   jungly, lavish, lawless, lax, liberal, licentious, loose, lush,
   luxuriant, many, maximal, much, mutineering, mutinous, noisy,
   nonrestrictive, numerous, obstreperous, opulent, out of control,
   out of hand, overabundant, overbounteous, overcopious,
   overexuberant, overflowing, overgenerous, overgrown, overlavish,
   overliberal, overluxuriant, overmuch, overnumerous, overplenteous,
   overplentiful, overplenty, overpopulated, overpopulous,
   overprolific, overrun, permissive, plenitudinous, plenteous,
   plentiful, plenty, plethoric, prevailing, prevalent, prodigal,
   productive, profuse, profusive, pullulating, rambunctious, rampant,
   rank, rebel, rebellious, reinless, replete, revolutional,
   revolutionary, rich, rife, robustious, roisterous, rollicking,
   rowdy, rumbustious, running over, seditionary, seditious,
   subversive, superabundant, swarming, teeming, terrorist, thick,
   traitorous, treasonable, tumultuous, turbulent, unbridled,
   unchecked, uncoerced, uncompelled, unconstrained, uncontrollable,
   uncontrolled, uncurbed, unforced, ungoverned, uninhibited,
   unmanageable, unmastered, unmeasured, unmuzzled, unreined,
   unrepressed, unreserved, unrestrained, unrestrictive, unruly,
   unsubdued, unsuppressed, unweeded, uproarious, violent, wanton,
   wealthy, weed-choked, weed-ridden, weedy, well-found,
   well-furnished, well-provided, well-stocked, wholesale, wild