Corrective system of exercising alone with CD playing (5,4)
I believe the answer is:
penal code
'corrective system' is the definition.
(system for punishment or correction)
'exercising alone with cd playing' is the wordplay.
'exercising' becomes 'pe' (abbreviation for Physical Education).
'with' means one lot of letters go next to another.
'playing' indicates anagramming the letters.
'alone' put after 'cd' is 'cdalone'.
'cdalone' is an anagram of 'nalcode'.
'pe'+'nalcode'='PENAL CODE'
'of' is the link.
(Another definition for penal code that I've seen is " Legal principles".)