Source : Webster's Revised Unabridged Dictionary (1913)

Ardor \Ar"dor\, n. [L. ardor, fr. ardere to burn: cf. OF. ardor,
   ardur, F. ardeur.] [Spelt also {ardour}.]
   1. Heat, in a literal sense; as, the ardor of the sun's rays.

   2. Warmth or heat of passion or affection; eagerness; zeal;
      as, he pursues study with ardor; the fought with ardor;
      martial ardor.

   3. pl. Bright and effulgent spirits; seraphim. [Thus used by
      Milton.]

   Syn: Fervor; warmth; eagerness. See {Fervor}.

Source : WordNet®

ardour
     n 1: a feeling of strong eagerness (usually in favor of a person
          or cause); "they were imbued with a revolutionary
          ardor"; "he felt a kind of religious zeal" [syn: {ardor},
           {elan}, {zeal}]
     2: intense feeling of love [syn: {ardor}]
     3: feelings of great warmth and intensity; "he spoke with great
        ardor" [syn: {ardor}, {fervor}, {fervour}, {fervency}, {fire},
         {fervidness}]