waterline

noun

special marking that indicates the draft of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures in order to safely maintain buoyancy, particularly with regard to the hazard of waves that may arise

Pronunciation: /ˈwɔːtə(ɹ)laɪn/

Etymology: From water + line.

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
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.
“Down here along the waterline, the Enterprise has a belt of thick antitorpedo armor. It's not too promising.”
The inner rim of the eyelid, just behind the lash line; primarily used in reference to the application of eyeliner.