Magnanimous English group backing rave (8)
I believe the answer is:
tolerant
'magnanimous' is the definition.
(thesaurus)
'english group backing rave' is the wordplay.
'english' becomes 'E' (abbreviation).
'group' becomes 'lot'.
'backing' says the letters should be written in reverse.
'rave' becomes 'rant' (synonyms).
'e'+'lot'='elot'
'elot' back-to-front is 'tole'.
'tole'+'rant'='TOLERANT'
(Other definitions for tolerant that I've seen before include "Learnt to be accepting of others" , "Patient; broad-minded" , "Broadminded, acceptance of others' beliefs" , "Liberal" , "Indulgent, lenient" .)