Smooth and sweet: "polite and cordial, with a mellifluous, well-educated voice"(H.W. Crocker III).
[Middle English, from Late Latin mellifluus : Latin mel, mell-, honey; see melit- in Indo-European roots + Latin -fluus, flowing; see bhleu- in Indo-European roots.] mel·lif'lu·ous·ly adv., mel·lif'lu·ous·ness n.
1432, from L.L. mellifluus "flowing with (or as if with) honey," from L. mel (gen. mellis) "honey" + -fluus "flowing," from fluere "to flow" (see fluent).