watermark
noun [ C ] uk/ˈwɔː.tə.mɑːk/ us/ˈwɑː.t̬ɚ.mɑːrk/
(PAPER)
（某些纸张上的）水印
a mark made in some types of paper during its production that can only be seen if it is held against the light
(RIVER/SEA)
水位标志
a mark showing the highest or lowest level that a river or the sea reaches