The rest stay, embracing United (7)
I believe the answer is:
residue
'the rest' is the definition.
('residue' can be a synonym of 'rest')
'stay embracing united' is the wordplay.
'stay' becomes 'reside' (I've seen this in other clues).
'embracing' indicates putting letters inside.
'united' becomes 'u'.
'reside' placed around 'u' is 'RESIDUE'.
(Other definitions for residue that I've seen before include "What is left over, remainder (7)" , "Deposit" , "Remains to be seen" , "Something left over" , "grounds" .)