One tune I'd rearranged (6)
I believe the answer is:
united
'one' is the definition.
('united' can be a synonym of 'one')
'tune i'd rearranged' is the wordplay.
'rearranged' is an anagram indicator.
'tune'+'id'='tuneid'
'tuneid' anagrammed gives 'UNITED'.
(Other definitions for united that I've seen before include "Got together" , "in league" , "Joined in marriage" , "Affiliated" , "... we stand, divided we fall" .)