Waterlines

Part of speech: noun

Definitions

1. A boundary or mark indicating the level of water in a vessel or structure
2. The lines observed on the hull of a boat that indicate where the waterline sits while afloat
3. A reference point used in construction or design to show the intended height of water in relation to buildings or infrastructure

Etymology: "Waterlines" is simply the plural of "waterline", a compound of "water" and "line" that is literally a line of water. The word's sense in construction, a level marking where water sits on a structure, grows naturally out of that picture, and the plural is used when more than one such level is in view, as when a building or dam shows several marks at different heights. The noun is built from two plain English words, with nothing borrowed or unusual in its making. In the shipbuilding sense it originally named the line where a vessel's hull meets the surface of the water, and that nautical usage gave the compound its basic shape before it was applied to structures on land.