Source : Webster's Revised Unabridged Dictionary (1913)

Smooth-tongued \Smooth"-tongued`\, a.
   Having a smooth tongue; plausible; flattering.

Source : WordNet®

smooth-tongued
     adj : artfully persuasive in speech; "a glib tongue"; "a
           smooth-tongued hypocrite" [syn: {glib}, {glib-tongued}]