Source : Webster's Revised Unabridged Dictionary (1913)

Dielectric \Di`e*lec"tric\, n. [Pref. dia- + electric.] (Elec.)
   Any substance or medium that transmits the electric force by
   a process different from conduction, as in the phenomena of
   induction; a nonconductor. separating a body electrified by
   induction, from the electrifying body.

Source : WordNet®

dielectric
     n : a material such as glass or porcelain with negligible
         electrical or thermal conductivity [syn: {insulator}, {nonconductor}]
         [ant: {conductor}]