Main stem is a term often used to describe the central part of a tree trunk, but it can also refer to other central and essential parts of various objects and systems. Synonyms for main stem include trunk, primary branch, main branch, main line, central vein, core, axis, backbone, and nucleus. The main stem of a river is also called the stream or channel, while the main stem of a highway is typically referred to as the mainline or through-route. The term can be applied to a variety of industries, such as agriculture, where the main stem could refer to the primary crop or growth of a plant. Overall, synonyms for main stem vary depending on the context in which it is used.