Imprison leaders of extreme nationalist cult over time (6)
I believe the answer is:
encage
'imprison' is the definition.
(I've seen this in another clue)
'leaders of extreme nationalist cult over time' is the wordplay.
'leaders of' says to take the initial letters.
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'time' becomes 'age' (an age is a period of time).
The first letters of 'extreme nationalist cult' is 'enc'.
'enc'+'age'='ENCAGE'
(Other definitions for encage that I've seen before include "Pen" , "Put behind bars" , "Bang up" .)