Pronunciation: (boosh'ing),[key] —n. 1. Elect.a lining for a hole, intended to insulate and protect from abrasion one or more conductors that pass through it.
2. Mach. a. a replaceable thin tube or sleeve, usually of bronze, mounted in a case or housing as a bearing.
b. a replaceable hardened steel tube used as a guide for various tools or parts, as a drill or valve rod.