Ration voting having ousted leader (5)
I believe the answer is:
allot
'ration' is the definition.
(I've seen this in another clue)
'voting having ousted leader' is the wordplay.
'voting' becomes 'ballot' (synonyms).
'having ousted leader' means to remove the first letter.
'ballot' with its first letter taken away is 'ALLOT'.
(Other definitions for allot that I've seen before include "Ration" , "Assign a share" , "deal" , "Distribute in portions" , "Dedicate" .)