a line marking the level reached by a body of water
"The ancient boat had a permanent scratch on its hull that served as a watermark, showing exactly how high the river rose during last year's flood."
a distinguishing mark impressed on paper during manufacture; visible when paper is held up to the light
"When I held the vintage document up against the sun, I could clearly see the faint watermark of an oak tree in the center."
A translucent design impressed on the surface of paper and visible when the paper is held to the light.
"When I held the document up to the lamp, a faint floral watermark became clearly visible in the center of the page."
To mark paper with a watermark.
"The artisan carefully pressed the damp paper against the raised metal design to imprint a subtle watermark before it dried completely."