The Collaborative International Dictionary of English v.0.48:

Smolder \Smol"der\, Smoulder \Smoul"der\, v. i. [imp. & p. p.
   Smolderedor Smouldered; p. pr. & vb. n. Smoldering or
   Smouldering.] [OE. smolderen; cf. Prov. G. sm["o]len,
   smelen, D. smeulen. Cf. Smell.]
   1. To burn and smoke without flame; to waste away by a slow
      and supressed combustion.
      [1913 Webster]

            The smoldering dust did round about him smoke.
                                                  --Spenser.
      [1913 Webster]

   2. To exist in a state of suppressed or smothered activity;
      to burn inwardly; as, a smoldering feud.
      [1913 Webster] Smolder

The Collaborative International Dictionary of English v.0.48:

Smoldering \Smol"der*ing\, Smouldering \Smoul"der*ing\, a.
   Being in a state of suppressed activity; quiet but not dead.
   [1913 Webster]

         Some evil chance
         Will make the smoldering scandal break and blaze.
                                                  --Tennyson.
   [1913 Webster] Smolderingness

WordNet (r) 3.0 (2006):

smoldering
    adj 1: showing scarcely suppressed anger; "her tone
           was...conversational although...her eyes were
           smoldering"- James Hensel [syn: smoldering,
           smouldering]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "smoldering":
   abeyant, ablaze, afire, aflame, aflicker, aglow, alight, apathetic,
   ardent, blazing, boiling, burning, candent, candescent, cataleptic,
   catatonic, comburent, conflagrant, dead, dopey, dormant, dull,
   flagrant, flaming, flaring, flat, flickering, foul, fuming,
   glowing, groggy, guttering, heavy, het up, hot, ignescent, ignited,
   in a blaze, in a glow, in abeyance, in flames, in suspense,
   inactive, incandescent, inert, inflamed, kindled, languid,
   languorous, latent, leaden, lifeless, live, living, logy, on fire,
   passive, phlegmatic, reeking, scintillant, scintillating,
   sedentary, seething, simmering, sizzling, slack, sleeping,
   sluggish, slumbering, smoking, sparking, stagnant, standing,
   static, suspended, tame, torpid, unaroused, unextinguished,
   unquenched