watermark (n.)youdaoicibaDictYouDict[watermark 词源字典]
also water-mark, 1708, "distinctive mark on paper," from water (n.1) + mark (n.1). Similar formation in German wassermarke. Not produced by water, but probably so called because it looks like a wet spot. The verb is recorded from 1866. Related: Watermarked.[watermark etymology, watermark origin, 英语词源]