Capital in its own right, or in retirement? (5)
I believe the answer is:
super
'capital' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for super that I've seen before include "Prefix meaning over or extremely" , "Jolly good" , "Exceptionally good" , "Great; wonderful" , "Informally great, really up there" .)