waterline

Noun

waterline (plural waterlines)

1. 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
2. A horizontal line indicating the shape of an airfoil.
3. A line showing where the water has been.
   • Down here along the waterline, the Enterprise has a belt of thick antitorpedo armor. It's not too promising.1992, Neal Stephenson, Snow Crash, page 391

   Synonyms:

   watermark

4. The line formed by where the water level of a body of water currently is: where the water's surface currently meets the bank; it may move higher or lower depending on the weather, tide, or season.
   • Near-synonym: water's edge
   • We are walking south-west, down a gently increasing slope, with the old farm buildings of the tiny hamlet of Villemiers [in the department of Charente] visible on the other side of the valley a kilometre away. The Transon [a tributary of the river Charente] meanders in the bottom of the valley...2015, Dave Goulson, A Buzz in the Meadow: The Natural History of a French Farm, Picador, →ISBN, page 14

   Synonyms:

   water's edge

5. The inner rim of the eyelid, just behind the lash line; primarily used in reference to the application of eyeliner.
6. A water pipeline.