At least one of two leaders in really autonomous principality (7)
I believe the answer is:
andorra
'principality' is the definition.
(I've seen this before)
'at least one of two leaders in really autonomous' is the wordplay.
'at least one of two' becomes 'and or' (and/or).
'leaders in' indicates taking the first letters.
The first letters of 'really autonomous' is 'ra'.
'andor'+'ra'='ANDORRA'
(Other definitions for andorra that I've seen before include "Radar on (anag) - European principality" , "Self-governing principality in Pyrenees" , "mountainous region" , "Autonomous principality in the Pyrenees" , "Principality between France and Spain" .)