Graduate to raise tax in secret vote (6)
I believe the answer is:
ballot
'secret vote' is the definition.
(I've seen this before)
'graduate to raise tax' is the wordplay.
'graduate' becomes 'BA' (someone with a Bachelor of Arts degree).
'to raise' says the letters should be written in reverse (in a down clue, letters go up).
'tax' becomes 'toll' (I've seen this in another clue).
'toll' backwards is 'llot'.
'ba'+'llot'='BALLOT'
'in' acts as a link.
(Other definitions for ballot that I've seen before include "Lottery (eg, for tickets)" , "Plebiscite" , "Voting procedure" , "Election" , "Lottery to allocate (tickets) among applicants" .)