They're of one accord (4)
I believe the answer is:
ayes
'they're' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'one accord' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'accord' becomes 'yes' (I can't justify this - if you can you should believe this answer much more).
'a'+'yes'='AYES'
'of' is the link.
Can you help me to learn more?
(Other definitions for ayes that I've seen before include "They express assent" , "Nautical affirmatives" , "Voting assents" , "The yes votes at committee meeting" , "Nautical positive responses" .)