Downwash

Part of speech: noun

Definitions

1. The downward airflow created around wings or rotors during lift generation affects nearby air dynamics and flight stability
2. The stream of air moving downward behind an aircraft wing or rotor as lift is produced
3. A downward current of air generated by the motion of wings or rotor blades during flight

Etymology: "Downwash" is a plain compound: "down" joined to "wash," meaning the air pushed downward behind a moving wing or rotor. The "down" half comes from an Old English word, and it traces back through Germanic to a root shared with words for hills and high ground. The "wash" half is the more interesting one. It descends from a Proto-Germanic verb meaning to wet or cleanse with water, which passed through Old English "wascan" and Middle English "waschen" before settling into modern "wash." Put together, the compound borrows the image of water flowing or sweeping over a surface and applies it to air. A wing passing through the atmosphere leaves a sweeping column of air moving downward, much as a stream of water washes across a stone. The term is a modern technical formation built from existing English parts, so it needs no foreign source, and the meaning follows directly from the two words rather than from any special story.