The term 'Smooth as Glass' can be summarized by the crossword solution 'SLEEK'. SLEEK is an adjective that describes something that is smooth, glossy, and graceful in appearance. It is often used to describe a person's hair or clothing, but it can also be used to describe the surface of an object, such as glass. In this case, the term 'Smooth as Glass' is referring to the smoothness of the glass surface.