Means of settling energy regulations (4)
I believe the answer is:
code
'regulations' is the definition.
(I've seen this before)
'means of settling energy' is the wordplay.
'means of settling' becomes 'cod' (abbreviation for 'cash on delivery'**).
'energy' becomes 'e' (physics symbol as in E=mco).
'cod'+'e'='CODE'
(Other definitions for code that I've seen before include "Body of laws" , "Collection of laws" , "Digest of laws" , "Program instructions" , "Cryptographic system" .)