United with everyone that is dead (6)
I believe the answer is:
allied
'united' is the definition.
('allied' can be similar in meaning to 'united')
'with everyone that is dead' is the wordplay.
'with' is a charade indicator (letters next to each other).
'everyone' becomes 'all' (I've seen this before).
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'dead' becomes 'd'.
'all' next to 'ie' is 'allie'.
'allie'+'d'='ALLIED'
(Other definitions for allied that I've seen before include "United through treaty" , "Joined for mutual benefit" , "(Of nations) working together" , "in concert" , "In league" .)