From The Collaborative International Dictionary of English v.0.48 [gcide]:
Dune \Dune\ (d[=u]n), n. [The same word as down: cf. D. duin.
See Down a bank of sand.]
A low hill of drifting sand usually formed on the coats, but
often carried far inland by the prevailing winds. [Written
also dun.]
[1913 Webster]
Three great rivers, the Rhine, the Meuse, and the
Scheldt, had deposited their slime for ages among the
dunes or sand banks heaved up by the ocean around their
mouths. --Motley.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
dune
n 1: a ridge of sand created by the wind; found in deserts or
near lakes and oceans [syn: dune, sand dune]