Millionaire bids to hold back European region (6)
I believe the answer is:
iberia
'european region' is the definition.
(I've seen this before)
'millionaire bids to hold back' is the wordplay.
'to hold' says the answer is hidden in the clue (I've seen 'held' mean this).
'back' is a reversal indicator.
'airebi' is hidden within 'millionaire bids'.
'airebi' reversed gives 'IBERIA'.
(Other definitions for iberia that I've seen before include "Old name for Spanish peninsula" , "Peninsula housing Spain and Portugal" , "European countries" , "W. European peninsula" , "West European peninsula" .)