Word Study
    rille
CIDE DICTIONARY
rille, n. [G. rille a furrow.]. 
                                            
                                         One of certain narrow, crooked valleys seen, by aid of the telescope, on the surface of the moon.                                                                                 [1913 Webster]                                                                                                                    
                                                                                    OXFORD DICTIONARY
rille, n.  (also rill) Astron.  a cleft or narrow valley on the moon's surface.
                    Etymology
                        G (as RILL)
                                    
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