Dark spirit on the rise leads to high tension (5)
I believe the answer is:
night
'dark' is the definition.
(it's dark at nighttime)
'spirit on the rise leads to high tension' is the wordplay.
'spirit' becomes 'gin' (alcoholic spirit).
'on the rise' is a reversal indicator (in a down clue, letters go up).
'leads to' says to put letters next to each other.
'high tension' becomes 'ht'.
'gin' in reverse letter order is 'nig'.
'nig'+'ht'='NIGHT'
(Other definitions for night that I've seen before include "death" , "See 1 Across" , "That's when it's darkest" , "The dark time" , "Time for turning" .)