water line

American  

[waw-ter lahyn] / ˈwɔ tər ˌlaɪn /

Or waterline

noun

1. Nautical. the part of the outside of a ship's hull that is just at the water level.

2. Naval Architecture. 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.

3. the line in which water at its surface borders upon a floating body.

4. water level.

5. Also called watermark.  a line indicating the former level or passage of water.

   A water line all around the cellar served as a reminder of the flood.

6. a pipe, hose, tube, or other line for conveying water.

7. waterline, 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.

---

water line British  

noun

1. a line marked at the level around a vessel's hull to which the vessel will be immersed when afloat

2. a line marking the level reached by a body of water

---

Etymology

Origin of water line

First recorded in 1615–25

Example Sentences

See Examples For:

water line

The walls of the valley at this point are steep, reaching up to 50m above the water line.

From BBC ● Aug. 28, 2026

Crews finished repairs Wednesday at noon and were working to re-pressurize and test the water line for any pathogens or contaminants, according to a statement from L.A.

From Los Angeles Times ● Aug. 7, 2025

The tank is connected to a high-pressure water line so that it can be refilled rapidly, thereby increasing the rate at which firefighting aircraft can perform water drops.

From Los Angeles Times ● Jul. 7, 2025

If you notice any patches of grass that seem to be growing faster than everything else, that might indicate a leaking buried water line.

From Seattle Times ● May 15, 2024

“The optimum population,” said Mustapha Mond, “is modelled on the iceberg—eight-ninths below the water line, one-ninth above.”

From "Brave New World" by Aldous Huxley