Everybody negotiating a nice partnership (8)
I believe the answer is:
alliance
'partnership' is the definition.
(I've seen this before)
'everybody negotiating a nice' is the wordplay.
'everybody' becomes 'all' (all people).
'negotiating' is an anagram indicator (I've seen 'negotiated' mean this).
'a'+'nice'='anice'
'anice' anagrammed gives 'iance'.
'all'+'iance'='ALLIANCE'
(Other definitions for alliance that I've seen before include "Association for mutual benefit" , "match?" , "Confederation" , "A joining of forces" , "Combination by treaty" .)