I. ˈril noun
Etymology: Dutch ril or Low German rille; akin to Old English rīth rivulet
Date: 1538
: a very small brook
II. intransitive verb
Date: 1610
: to flow like a rill
III. ˈril noun
or rille ˈril, ˈri-lə
Etymology: German Rille, literally, channel made by a small stream, from Low German, rill
Date: 1868
: any of several long narrow valleys on the moon's surface