Nearest neighbours exemplify tact, initially holding vote (4)
I believe the answer is:
next
'nearest' is the definition.
(I've seen this before)
'neighbours exemplify tact initially holding vote' is the wordplay.
'initially' says to take the initial letters.
'holding' means one lot of letters goes inside another.
'vote' becomes 'x' (how votes are marked).
The first letters of 'neighbours exemplify tact' is 'net'.
'net' going around 'x' is 'NEXT'.
(Other definitions for next that I've seen before include "Nearest following" , "Coming nearest in order - come, please!" , "Coming immediately" , "shop" , "Soonest encountered" .)