ETYM The same word as down: cf. Dutch duin. Related to Down a bank of sand.
A ridge of sand created by the wind; found in deserts or near lakes and oceans; SYN. sand dune.
Mound or ridge of wind-drifted sand common on coasts and in sandy deserts. Loose sand is blown and bounced along by the wind, up the windward side of a dune. The sand particles then fall to rest on the lee side, while more are blown up from the windward side. In this way a dune moves gradually downwind.
In sandy deserts, the typical crescent-shaped dune is called a barchan. Seif dunes are longitudinal and lie parallel to the wind direction, and star-shaped dunes are formed by irregular winds.