The educational establishment Edward joined (6)
I believe the answer is:
united
'joined' is the definition.
(synonyms)
'the educational establishment edward' is the wordplay.
'the educational establishment' becomes 'uni' (I've seen this before).
'edward' becomes 'ted'.
'uni'+'ted'='UNITED'
(Other definitions for united that I've seen before include "See 14" , "Agreed" , "Football team" , "Merged into one" , "in league" .)