Vote of dissent (3)
I believe the answer is:
nay
'vote of dissent' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nay that I've seen before include "In point of fact - a parliamentary vote against" , "No (dialect); or rather" , "Indeed" , "Refusal" , "Archaic negative" .)