waterline

IPA: wˈɔtɝɫaɪn

(nautical) A line formed by the surface of the water on the hull of a ship when she is afloat; any of a series of short lines marked on the hull to show where the waterline would be under different loadings.
(aviation) A horizontal line indicating the shape of an airfoil.
A line showing where the water has been, usually a line separating dry land and wet areas; a watermark or tidemark.
(cosmetics) The inner rim of the eyelid, just behind the lash line; primarily used in reference to the application of eyeliner.

water line

IPA: wˈɔtɝɫˈaɪn

(shipbuilding) the outline of a horizontal section of a vessel, as when floating in the water.
(shipbuilding) Any one of certain lines of a vessel, model, or plan, parallel with the surface of the water at various heights from the keel. In a half-breadth plan, the water lines are outward curves showing the horizontal form of the ship at their several heights; in a sheer plan, they are projected as straight horizontal lines.
(nautical) Any one of several lines marked upon the outside of a vessel, corresponding with the surface of the water when she is afloat on an even keel. The lowest line indicates the vessel's proper submergence when not loaded, and is called the light water line; the highest, called the load water line, indicates her proper submergence when loaded.
The line corresponding to the surface of the water touching any submerged object or body.
The level at which water meets land along the shore of a body of water.