D defs.my
Entry 2 senses Webster, 1913

Insulator

/ĭn'-səl-ātˌ-ẽr/ · In·su·la·tor · IPA /ˈɪn.s(j)ə.leɪ.tə(ɹ)/
01 n. One who, or that which, insulates.
  1. 1.
    One who, or that which, insulates.
  2. 2.
    A substance or object that insulates; a nonconductor; as, polyurethane foam is a popular thermal insulator.(Elec. & Thermotics)