Unctuous:
- characterized by excessive piousness or moralistic fervor, especially in an affected manner; excessively smooth, suave, or smug.
- of the nature of or characteristic of an unguent or ointment; oily; greasy.
- having an oily or soapy feel, as certain minerals. [Dictionary.com]
Heard on America’s Test Kitchen in reference to their version of Charlotte Russe. I’ve also run across it in fiction, usually in a slightly repulsive context.
