Source : Webster's Revised Unabridged Dictionary (1913)

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.

   2. Having a smooth, greasy feel, as certain minerals.

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

Source : WordNet®

unctuous
     adj : unpleasantly and excessively suave or ingratiating in manner
           or speech; "buttery praise"; "gave him a fulsome
           introduction"; "an oily sycophantic press agent";
           "oleaginous hypocrisy"; "smarmy self-importance"; "the
           unctuous Uriah Heep" [syn: {buttery}, {fulsome}, {oily},
            {oleaginous}, {smarmy}]