True origin of magic kingdom (5)
I believe the answer is:
realm
'kingdom' is the definition.
(thesaurus)
'true origin of magic' is the wordplay.
'true' becomes 'real' ('real' can be similar in meaning to 'true').
'origin of' indicates taking the first letters.
The initial letter of 'magic' is 'm'.
'real'+'m'='REALM'
(Other definitions for realm that I've seen before include "Kingdom could be lamer" , "Peers are possessed by this" , "Area of influence" , "the UK, perhaps" , "Dominion" .)