The Collaborative International Dictionary of English v.0.48:

Unctuous \Unc"tu*ous\ (?; 135), a. [F. onctueux, LL. unctuosus,
   fr. L. unctus anointment, fr. ungere, unctum, to anoint. See
   Unguent.]
   1. Of the nature or quality of an unguent or ointment; fatty;
      oily; greasy. "The unctuous cheese." --Longfellow.
      [1913 Webster]

   2. Having a smooth, greasy feel, as certain minerals.
      [1913 Webster]

   3. Bland; suave; also, tender; fervid; as, an unctuous
      speech; sometimes, insincerely suave or fervid.
      [1913 Webster] -- Unc"tu*ous*ly, adv. --
      Unc"tu*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unctuously
    adv 1: in an unctuous manner [syn: unctuously, smarmily,
           fulsomely]