Prevalent depression in the countryside? (4)
I believe the answer is:
vale
'countryside?' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'prevalent depression in' is the wordplay.
'in' indicates the answer is hidden within the clue.
'VALE' is hidden in the letters of 'prevalent depression'.
'the' is the link.
Can you help me to learn more?
(Other definitions for vale that I've seen before include "Maida -, N. London area; farewell (archaic)" , "Valley" , "Glen; goodbye!" , "Long depression containing a river" , "'''Sweet ... of Avoca, how calm could I rest'' (Moore) (4)'" .)