Clean river? (3)
I believe the answer is:
lea
'river?' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'clean' is the wordplay.
'LEA' is hidden within the letters.
However, I am unsure how this is indicated.
Can you help me to learn more?
(Other definitions for lea that I've seen before include "Open area of grassy or arable land" , "Open pasture" , "Grazing land" , "Poetically, a piece of meadow or pasture" , "Meadow (poetic)" .)