Unctuous \UNGK-choo-us\ , adjective;
1. Of the nature or quality of an unguent or ointment; fatty; oily; greasy
2. Having a smooth, greasy feel, as certain minerals
3. Insincerely or excessively suave or ingratiating in manner or speech; marked by a false or smug earnestness or agreeableness
This word dates to the late 14th century from Old French unctueus, which derives from Middle Latin unctuosus ("greasy"). The Middle Latin word is based on Latin unctus ("act of annointing") from the past participle stem of unguere ("to annoint"), which comes from the Proto-Indo-European base *ongw- ("to salve, anoint"). For some reason, the incarnation of that Proto-Indo-European base in various Indo-European languages seems to be either "anoint" or "butter."
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Saturday, April 2
Etymologies come from the Oxford English Dictionary and/or Etymonline.com