noun (n)

• a material such as glass or porcelain with negligible electrical or thermal conductivity(noun.substance)

  Synonym:
  insulator, nonconductor
  Antonym:
  conductor
  

  source: wordnet30
• 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.(noun)

  source: webster1913