water line

or wa·ter·line

noun

Nautical. the part of the outside of a ship's hull that is just at the water level.
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.Compare load line, Plimsoll line.
the line in which water at its surface borders upon a floating body.

water level(def 2).
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.
a pipe, hose, tube, or other line for conveying water.

Origin of water line

First recorded in 1615–25

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for waterline

Contemporary Examples of waterline

Meanwhile, the rest of hull is wide at the waterline and slopes inward.
Can the Navy's $12 Billion Stealth Destroyer Stay Afloat?
Dave Majumdar
October 22, 2014
His last novel, Waterline was the story of a one-time shipbuilder in the Glasgow yards, now broken by loss.
Granta’s List of Best British Novelists Today
Lucy Scholes
April 15, 2013

Historical Examples of waterline

One man said the ship had been struck above the waterline and would float.
Tom Slade with the Colors
Percy K. Fitzhugh
A moment later, and the whole schooner was ablaze, from waterline to masthead.
The Black Buccaneer
Stephen W. Meader
Five of the nine left of the Waterline outfit drove the herd.
Rimrock Trail
J. Allan Dunn
He had seen them before on their first unsuccessful trip to the Waterline.
Rimrock Trail
J. Allan Dunn
He drove me off'n the Waterline, him an' the ones that hang with him.
Rimrock Trail
J. Allan Dunn

British Dictionary definitions for waterline

water line

noun

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

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for waterline

1620s, line where the water rises to on the hull of a ship afloat, from water (n.1) + line (n.).