- the part of the outside of a ship's hull that is just at the water level.
- any of a series of lines on the hull plans of a vessel representing the level to which the vessel is immersed or the bottom of the keel.
- the line in which water at its surface borders upon a floating body.
- water level (def. 2).
- a line indicating the former level or passage of water: A water line all around the cellar served as a reminder of the flood.
- a pipe, hose, tube, or other line for conveying water.
- the slightly wet inner rim of skin between the upper or lower eyelashes and the eye, especially with reference to the use of eyeliner: Apply pencil eyeliner to your upper and lower waterlines.
- a line marked at the level around a vessel's hull to which the vessel will be immersed when afloat
- a line marking the level reached by a body of water
