Noah Webster's Dictionary (n.) Quality or state of being smooth.

Multi-Version Concordance Smoothness (2 Occurrences) Proverbs 6:24 To keep thee from the evil woman, From the flattery of the foreigner's tongue. (See JPS) Proverbs 7:21 With her much enticement she beguiled him; with the smoothness of her lips she constrained him. (DBY)