Poetic lowland (4)
I believe the answer is:
vale
'poetic lowland' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for vale that I've seen before include "'''Sweet ... of Avoca, how calm could I rest'' (Moore) (4)'" , "Valley" , "Maida -, N. London area; farewell (archaic)" , "Glen; goodbye!" , "Trough between ridges" .)