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):

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