A material that does not easily transmit energy, such as electric current or heat. Materials such as wood, plastic, and ceramics are insulators. Fiberglass is an example of a heat insulator. (Compareconductor.)
Main Entry: in·su·la·tor Pronunciation: 'in(t)-s&-"lAt-&r Function: noun : a material that is used to provide insulation;also: a device made of such material