1 In this sense it is nearly synonymous with synopsis. ( 2 n.) The tracing of things to their source, and the resolving of knowledge into its original principles. ( 3 n.) A syllabus, or table of the principal heads of a discourse, disposed in their natural order.
A lightning rod or lightning conductor is a iron rod that is used to make lightning strike it, rather than strike something else. It is part of a lightning protection system. Such a system is made of many such rods. These rods are usually placed at high points of buildings and structures.
A third purpose of the rod is to serve as a counting and inspection mechanism. It's actually where the Old Testament term passing under the rod stems from (Ezekiel 20:37). So not only is it important for the flock to remain under the shepherd's control and authority, but it's doubly important that the flock be subjected to the shepherd's careful and precise examination.