Vote, maybe, or the opposite (4)
I believe the answer is:
veto
'the opposite' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'vote maybe' is the wordplay.
'maybe' is an anagram indicator.
'vote' with letters rearranged gives 'VETO'.
'or' acts as a link.
Can you help me to learn more?
(Other definitions for veto that I've seen before include "Vote that blocks a decision" , "Power to reject legislation" , "An overriding negative vote" , "Right to reject a decision" , "Overrule, forbid" .)