Over in part of Spain, a modern craze (5)
I believe the answer is:
mania
'craze' is the definition.
(I've seen this in another clue)
'over in part of spain a modern' is the wordplay.
'over' shows that the letters should be reversed in order.
'in part of' indicates a hidden word (I've seen 'in part' mean this).
'ainam' is hidden within 'spain a modern'.
'ainam' backwards is 'MANIA'.
(Other definitions for mania that I've seen before include "Mental disorder that results in excessive or violent responses" , "Frenzy" , "Obsessive enthusiasm" , "Over-enthusiasm" , "thing" .)