water line vs watermark

water line

noun
  • The level at which water meets land along the shore of a body of water. 

  • 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. 

  • 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. 

  • The line corresponding to the surface of the water touching any submerged object or body. 

  • the outline of a horizontal section of a vessel, as when floating in the water. 

watermark

noun
  • A mark indicating the level to which water has risen. 

  • A translucent design impressed on the surface of paper and visible when the paper is held to the light. 

  • A logo superimposed on a digital image, a television broadcast, etc. 

  • A value stored in a datafile to ensure its integrity, so that if the file's contents are changed then the watermark will no longer match the contents. 

verb
  • To mark paper with a watermark. 

  • To mark a datafile with a digital watermark. 

How often have the words water line and watermark occurred in a corpus of books? (source: Google Ngram Viewer )