Reckon Italian song not initially oppressive (12)
I believe the answer is:
totalitarian
'oppressive' is the definition.
(thesaurus)
'reckon italian song not initially' is the wordplay.
'reckon' becomes 'total' (I've seen this before).
'italian' becomes 'it' (common abbreviation).
'song' becomes 'aria' (piece of music in an opera).
'initially' suggests taking the first letters.
The initial letter of 'not' is 'n'.
'total'+'it'+'aria'+'n'='TOTALITARIAN'
(Other definitions for totalitarian that I've seen before include "Despotic" , "(Of states) extremely dictatorial" , "Allowing no opposition" , "Tyrannical" , "Of ultimate-State-control system" .)