wa ‧ ter ‧ mark /ˈwɔːtəmɑːk $ ˈwɒːtərmɑːrk, ˈwɑː-/ BrE AmE noun [countable]
1 . a special design put onto paper, especially bank notes, that can only be seen when you hold it up to the light
bear/carry a watermark
The sheet bears the watermark ‘1836’.
2 . a special mark contained in electronic documents, pictures, music etc that is used to stop people from copying them:
The card has a digital watermark detectable only by electronic cash dispensers.
3 . high watermark especially American English the high watermark of a particular process is its most successful time or achievement SYN high point
high watermark of
Reagan’s presidency may prove to have been the high watermark of the US-Israeli alliance.
4 . high/low watermark American English a line showing the highest or lowest levels of the sea SYN tide-mark British English