Law officer developing a tolerant energy (8,7)
I believe the answer is:
attorney general
'law officer' is the definition.
(attorney general is a kind of law officer)
'developing a tolerant energy' is the wordplay.
'developing' indicates anagramming the letters.
'a'+'tolerant'+'energy'='atolerantenergy'
'atolerantenergy' is an anagram of 'ATTORNEY GENERAL'.
(Other definitions for attorney general that I've seen before include "Crown legal officer" , "Lawman" , "Chief law officer" , "chief legal officer" , "Senior lawyer" .)