Vale seen in a single night (4)
I believe the answer is:
glen
'vale' is the definition.
(I know that glen is a type of vale)
'in a single night' is the wordplay.
'in' says the answer is hidden in the clue.
'GLEN' is hidden within 'single night'.
'seen' acts as a link.
(Other definitions for glen that I've seen before include "Scottish mountain valley" , "Campbell perhaps" , "Narrow valley with a stream" , "Highland valley" , "Depression in Scotland" .)