A Republican state, one of the old Confederate ones (8)
I believe the answer is:
arkansas
'one of the old confederate ones' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'a republican state' is the wordplay.
'republican' becomes 'r' (abbreviation).
'state' becomes 'kansas' (Kansas is an example).
'a'+'r'+'kansas'='ARKANSAS'
Can you help me to learn more?
(Other definitions for arkansas that I've seen before include "American state, capital Little Rock" , "State of S. central US" , "used to be a Land of Opportunity" , "25th US state" , "Confederate state in the American Civil War" .)