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 rod is the part that connects between the crank and the piston. The usual meaning of throw a rod means it has broken off and is now sticking out through a hole in the engine block, which means you need a whole new engine. That's why you don't drive if the oil light comes on, or if you hear metallic knocking sounds.