Small brook (6)
'small brook' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rill that I've seen before include "Little stream" , "Brooklet" , "Burn" , "Small brook" , "Flow of water" .)
'small brook' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for runnel that I've seen before include "Rivulet" , "A small stream or brook" , "Small stream or gutter" , "Brook; gutter" .)