United improved, Solskjaer finally sacked (6)
I believe the answer is:
allied
'united' is the definition.
(similar in meaning)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for allied that I've seen before include "Connected, related" , "Joined together for a purpose" , "in concert" , "Joined for mutual benefit" , "Affiliated" .)