“从大气中通过凝结沉积的水蒸气，特别是在夜间”，中世纪英语 deaw, deu，源自古英语 deaw，再往前追溯到原始日耳曼语 *dawwaz（同源词还有古撒克逊语 dau、古弗里斯语 daw、中世纪荷兰语 dau、古高地德语 tau、现代德语 Tau、古诺尔斯语 dögg，意为“露水”）。可能源自原始印欧语词根 *dheu-，意为“流动”（同源词还有梵语 dhavate，意为“流动，奔跑”）。
在晚期古英语中，这个词被用作比喻，形容某物清新宜人（如露水），或者唤起清晨和青春的气息（约1530年代）。作为动词时，意为“用露水湿润”或“像露水一样湿润”，古英语 deawian。
The formation of dew is explained by the loss of heat by bodies on the earth's surface through radiation at night, by which means they and the air immediately about them are cooled below the dew-point ....Dew is thus deposited chiefly on bodies which are good radiators and poor conductors of heat, like grass; hence also it appears chiefly on calm and clear nights--that is, when the conditions are most favorable for radiation. It never appears on nights both cloudy and windy. In winter dew becomes hoar frost. [Century Dictionary]
露水的形成可以通过夜间地表物体通过辐射散失热量来解释，这样它们及其周围的空气温度就会降到露点以下……因此，露水主要沉积在那些良好的辐射体和较差的热导体上，比如草；这也是为什么露水主要出现在宁静而晴朗的夜晚——即辐射条件最有利的时候。在多云和多风的夜晚，露水几乎不会出现。冬天，露水会变成白霜。[《世纪词典》]
