Stop setback for majority of poll? (4)
I believe the answer is:
veto
'stop' is the definition.
(I've seen this before)
'setback for majority of poll?' is the wordplay.
'setback' is a reversal indicator.
'for' becomes 'ev' (I can't justify this - if you can you should believe this answer much more).
'majority of' means to remove the last letter.
'poll?' becomes 'top' (poll is a kind of top).
'ev' backwards is 've'.
'top' with its last letter removed is 'to'.
've'+'to'='VETO'
Can you help me to learn more?
(Other definitions for veto that I've seen before include "Literally, 'I forbid'" , "Rule out" , "Right to reject a decision" , "Formally forbid" , "Throw out" .)