The Collaborative International Dictionary of English v.0.48:

Mellifluous \Mel*lif"lu*ous\, a. [L. mellifluus; mel, mellis,
   honey (akin to Gr. ?, Goth. milip) + fluere to flow. See
   Mildew, Fluent, and cf. Marmalade.]
   Flowing as with honey; smooth; flowing sweetly or smoothly;
   as, a mellifluous voice. -- Mel*lif"lu*ous*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mellifluous
    adj 1: pleasing to the ear; "the dulcet tones of the cello"
           [syn: dulcet, honeyed, mellifluous, mellisonant,
           sweet]