One from southern Europe racing round with hidden energy (7)
I believe the answer is:
grecian
'one from southern europe' is the definition.
Although both the answer and definition are adjectives, I can't understand how they can define each other.
'racing round with hidden energy' is the wordplay.
'round' is an anagram indicator.
'with hidden' means one lot of letters goes inside another (inserted letters are hidden inside).
'energy' becomes 'e' (physics symbol as in E=mc2).
'racing' is an anagram of 'grcian'.
'grcian' enclosing 'e' is 'GRECIAN'.
Can you help me to learn more?
(Other definitions for grecian that I've seen before include "of ancient Olympia, say" , "Hellene" , "Attic" , "Hellenic" , "Relating to ancient Greece" .)