The Collaborative International Dictionary of English v.0.48:

Glib \Glib\ (gl[i^]b), a. [Compar. Glibber (gl[i^]b"b[~e]r);
   superl. Glibbest (gl[i^]b"b[e^]st).] [Prob. fr. D.
   glibberen, glippen, to slide, glibberig, glipperig, glib,
   slippery.]
   [1913 Webster]
   1. Smooth; slippery; as, ice is glib. [Obs.]
      [1913 Webster]

   2. Speaking or spoken smoothly and with flippant rapidity;
      fluent; voluble; as, a glib tongue; a glib speech.
      [1913 Webster]

            I want that glib and oily art,
            To speak and purpose not.             --Shak.

   Syn: Slippery; smooth; fluent; voluble; flippant.
        [1913 Webster]