The riches of the law (6)
I believe the answer is:
wealth
'the riches' is the definition.
('wealth' can be a synonym of 'riches')
'of the law' is the wordplay.
'of' indicates an anagram (the answer comes from or 'of' the letters).
'the'+'law'='thelaw'
'thelaw' is an anagram of 'WEALTH'.
(Other definitions for wealth that I've seen before include "An abundance of valuable possessions or money" , "capital" , "Prosperity" , "State of luxury" , "Possessions and resources" .)