Right for electoral system to cover vote conclusively (6)
I believe the answer is:
proper
'right' is the definition.
(I know that right can be written as proper)
'for electoral system to cover vote conclusively' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'electoral system' becomes 'pr' (proportional representation).
'to cover' is an insertion indicator.
'conclusively' suggests the final letters (the letter which concludes the word).
The last letter of 'vote' is 'e'.
'pr' enclosing 'e' is 'per'.
'pro'+'per'='PROPER'
(Other definitions for proper that I've seen before include "Conforming to etiquette" , "Right or suitable" , "Real; genuine" , "Correct, decent" , "Right, correct or appropriate" .)