Established rule in Isle of Man following a vote (5)
I believe the answer is:
axiom
'established rule' is the definition.
(I've seen this in another clue)
'isle of man following a vote' is the wordplay.
'isle' becomes 'i' (geographical abbreviation).
'of' becomes 'o''.
'man' becomes 'm' (M is an abbreviation for male or masculine).
'following' is a charade indicator (letters next to each other).
'vote' becomes 'x' (how votes are marked).
'i'+'o'+'m'='iom'
'a'+'x'='ax'
'iom' put after 'ax' is 'AXIOM'.
'in' is the link.
(Other definitions for axiom that I've seen before include "Dictum" , "Generally accepted truism" , "saw" , "that goes without saying" , "Maxim, aphorism" .)