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[ril] /rɪl/
noun, Astronomy
any of certain long, narrow, straight or sinuous trenches or valleys observed on the surface of the moon.
Also, rille.
1885-90; < German Rille; see rill1 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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British Dictionary definitions for rille


a brook or stream; rivulet
a small channel or gulley, such as one formed during soil erosion
Also rille. one of many winding cracks on the moon
Word Origin
C15: from Low German rille; related to Dutch ril
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for rille



"small brook, rivulet," 1530s, from or related to Dutch and Frisian ril, Low German rille "groove, furrow, running stream," probably from Proto-Germanic *ril- (cf. Old English rið, riþe "brook, stream," which survives only in dialects), a diminutive form from PIE root *reie- "to run, flow" (see Rhine).

Online Etymology Dictionary, © 2010 Douglas Harper
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Encyclopedia Article for rille

any of various valleys or trenches on the surface of the Moon. The term was introduced by early telescopic observers-probably the German astronomer Johann Schroter about 1800-to denote such lunar features. The word rima (from Latin, "fissure") is often used for the same kind of features.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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