Origins
The word 'dew' descends from Old English 'dēaw,' one of the most ancient atmospheric terms in the English language. The Old English form comes from Proto-Germanic *dawwą, with cognates in German 'Tau,' Dutch 'dauw,' Old Norse 'dogg,' and Gothic '*daggw' (attested only in compounds). The Proto-Germanic word traces to PIE *dhewh₂-, a root meaning 'to flow,' 'to run,' 'to rise as vapor,' or 'to smoke.' This root is one of the most fascinating in Indo-European linguistics because it connects water, vapor, and smoke through the concept of exhalation — something rising from a surface.
The same PIE root produced Latin 'fūmus' (smoke) — source of English 'fume,' 'fumigate' (to apply smoke), 'perfume' (literally 'through smoke,' originally referring to fragrance released by burning), and 'fumble' (possibly). Sanskrit 'dhūmá' (smoke) is the same word. Greek 'thýmos' (spirit, breath, soul — the animating vapor of life) may also be related, though this is debated. If correct, then 'dew,' 'fume,' and 'thymus' (the organ named after the Greek word for a warty excrescence resembling a thyme bud, but possibly influenced by 'thýmos') are all cousins.
The formation of dew was a mystery to ancient observers. Aristotle discussed it in his Meteorologica, correctly noting that dew formed on calm, clear nights but not on windy or cloudy ones. The scientific explanation — that dew forms when surfaces cool below the dew point temperature, causing water vapor in the contact layer of air to condense — was not fully articulated until the work of Charles Leroy (1751) and William Charles Wells (1814). Wells's 'Essay on Dew' (1814) is considered a classic of scientific reasoning, praised by John Herschel as a model of inductive method.
Latin Roots
Dew has been symbolically important across cultures. In the Hebrew Bible, dew is a sign of divine blessing and fertility. Deuteronomy 33:28 describes Israel dwelling in a land of 'grain and new wine, whose heavens drop dew.' In the story of Gideon (Judges 6:36–40), the 'fleece of dew' serves as a divine sign. In classical mythology, Eos (Aurora), the goddess of dawn, was said to shed tears that became the morning dew — a poetic explanation for why dew appears at dawn.
In English poetry, dew has been one of the most persistent metaphors for freshness, purity, brevity, and the transience of life. Andrew Marvell's 'On a Drop of Dew' (1681) uses the dewdrop as a metaphor for the soul, temporarily resting on the leaf of the body before returning to heaven. Shakespeare uses dew repeatedly as a symbol of morning, youth, and delicacy. The phrase 'dewy-eyed' means naive or sentimentally fresh. 'Mountain Dew' — before it became a soft drink brand (1940s) — was Appalachian slang for illegally distilled whiskey, the 'dew' of the mountain stills.
The compound 'dewdrop' dates from Old English. 'Dewfall' refers to the time of evening when dew begins to form. 'Dewy' as an adjective meaning fresh and innocent dates from the sixteenth century. The personal name 'Dewey' is unrelated — it is a Welsh name from 'Dewi' (David).
Legacy
Ecologically, dew is more important than its small volume might suggest. In arid and semi-arid environments, dew can be a significant source of moisture for plants and small animals. Some organisms, such as the Namib Desert beetle (Stenocara gracilipes), have evolved specialized surfaces that harvest dew from fog, collecting water in one of the driest places on Earth. Human dew-harvesting technologies, inspired by such biological adaptations, are being developed as supplementary water sources in water-scarce regions.