A mark indicating the height to which water has risen, or at which it has stood; the usual limit of high or low water. [1913 Webster]
A letter, device, or the like, wrought into paper during the process of manufacture. [1913 Webster]
" “The watermark in paper is produced by bending the wires of the mold, or by wires bent into the shape of the required letter or device, and sewed to the surface of the mold; -- it has the effect of making the paper thinner in places. The old makers employed watermarks of an eccentric kind. Those of Caxton and other early printers were an oxhead and star, a collared dog's head, a crown, a shield, a jug, etc. A fool's cap and bells, employed as a watermark, gave the name to foolscap paper; a postman's horn, such as was formerly in use, gave the name to post paper.” Tomlinson. " Tomlinson. [1913 Webster]
See Water line, 2. [1913 Webster]

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OXFORD DICTIONARY

watermark, n. & v.
--n. a faint design made in some paper during manufacture, visible when held against the light, identifying the maker etc.
--v.tr. mark with this.

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THESAURUS

watermark

Plimsoll line, Plimsoll mark, birthmark, blaze, blemish, blotch, brand, caste mark, check, checkmark, cicatrix, cut, dapple, discoloration, dot, earmark, engraving, fleck, flick, freckle, gash, graving, hack, high-water mark, jot, lentigo, load waterline, macula, mark, marking, mole, mottle, nevus, nick, notch, patch, point, polka dot, prick, puncture, scar, scarification, score, scotch, scratch, scratching, speck, speckle, splash, splotch, spot, stain, stigma, strawberry mark, tattoo, tattoo mark, tick, tidemark, tittle, waterline

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