Head over heels, finally passionate (4)
I believe the answer is:
nuts
'passionate' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
'head over heels finally' is the wordplay.
'head' becomes 'nut' (informal term for somebody's head).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'finally' says to take the final letters.
The final letter of 'heels' is 's'.
'nut'+'s'='NUTS'
Can you help me to learn more?
(Other definitions for nuts that I've seen before include "Crazy; food" , "Nibbles" , "Potty" , "Mast - mad" , "Bolt securers" .)