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.
The conductor cables and ground rods are the most important components of a lightning protection system, accomplishing the main objective of diverting lightning current safely past a structure. The 'lightning rods' themselves, that is, the pointy vertically-oriented terminals along the edges of roofs, do not play much of a role in the functionality of the system.