main

When used as an adjective, "main" usually comes before the noun it describes (e.g., "the main street"). It is one of the most common words used to describe the most important part of something. As a noun referring to pipes, it is often paired with a specific resource, such as "water main" or "gas main." In this context, it refers to the large central pipe that feeds smaller pipes. The use of "main" to mean the ocean is very old-fashioned and rare in modern conversation. You will mostly find it in poetry, historical novels, or specific names like "the Spanish Main."