Rage at English being self-restrained (9)
I believe the answer is:
temperate
'self-restrained' is the definition.
(thesaurus)
'rage at english' is the wordplay.
'rage' becomes 'temper' (I've seen this before).
'english' becomes 'e' (abbreviation).
'temper'+'at'+'e'='TEMPERATE'
'being' is the link.
(Other definitions for temperate that I've seen before include "Calm" , "Showing self-restraint" , "sober" , "With mild climate" , "benign" .)